Three cans of tuna and 12 corn tostadas feed four people, and whether the shells stay crisp comes down to how hard you press the tuna dry. A tostada is a corn tortilla fried or baked until it’s flat, rigid and crisp, then piled with a topping like an open-faced taco. In Mexico, tostadas de atún, made with canned tuna, are a standard on the meatless Fridays of Lent and a go-to snack when people drop by, because the whole thing is pantry food and nothing gets cooked. This is the ceviche-style version, bright with lime, tomato, onion and chile, plus the creamy mayo one, what to buy in a US or UK supermarket, and how to keep the shells from going soft.
Tuna tostadas at a glance
How do you make Mexican tuna tostadas? Drain three 5 oz (140 g) cans of water-packed tuna very well and flake it. Toss it with seeded tomato and cucumber, chopped onion, serrano and cilantro, ¼ cup (60 ml) of lime juice and a little salt, and chill for 10 minutes. Spoon off the liquid and pile it onto corn tostadas spread with avocado. 30 minutes for 4 servings of 3 tostadas.
What you get. A cold, tangy, lightly spicy topping, with shreds of tuna and crisp diced vegetables, on a shell that should still crack when you bite it. Think of it as a Mexican tuna salad without the mayo, eaten off a corn cracker the size of your palm.
It isn’t raw fish ceviche. Canned tuna is already cooked, so the lime here is seasoning. A true Mexican fish ceviche uses raw white fish “cooked” in lime for 20 to 30 minutes, and shrimp ceviche works the same way with shrimp.
Time and effort. 30 minutes with bought shells: about 20 of chopping and 10 of chilling. Add 15 minutes if you bake your own. Easy: there’s no doneness to judge, only draining and timing.
Which canned tuna to buy, US and UK
Water-packed beats oil-packed here. Tuna in water gives a clean mix that soaks up the lime. Oil-packed tuna leaves a slick at the bottom of the bowl that ends up in the shell, and adds roughly 80 calories per serving. If oil-packed is what you have, drain it just as thoroughly and use 1 tbsp less lime.
Chunk light is fine. In a mix with lime and vegetables, I can’t tell chunk light tuna from solid white albacore on a tostada, and chunk light costs less. Very finely flaked tuna turns pasty; if that’s all you can find, add a little extra tomato and cucumber.
How much is in a can. A US 5 oz can and a Mexican 140 g can hold roughly 3¼ to 3½ oz (90 to 100 g) of tuna once drained; the rest is water. UK cans are usually 145 g, and the label lists the drained weight. Whatever the size, you want about 10 oz (280 g) drained for 12 tostadas.
Draining it properly. Tip it into a sieve and press with a spoon, or press the lid down into the open can and tilt it over the sink. It’s done when pressing gives you no more drips. That one minute is what keeps the shells crisp.
Swaps for a US or UK kitchen
| If you can’t find | Use | What changes |
|---|---|---|
| Serrano chile | 1 jalapeño per serrano, or a UK green finger chilli | Jalapeño is milder and fleshier |
| Plum tomatoes | Any firm salad tomato, seeded | Larger round tomatoes release more water |
| Limes | Lemons | Works, but tastes more floral and less sharp |
| Cilantro | Flat-leaf parsley | Fresh, but not the classic flavor |
| Cucumber | 2 oz (50 g) more tomato | Less crunch and freshness |
Store-bought or homemade tostada shells
Where to buy them. In the US, packaged corn tostadas sit in the Hispanic or international aisle of most supermarkets, next to the tortillas. In the UK they’re harder to find in supermarkets; Mexican grocers and online shops carry them, and they’re easy to make from corn tortillas. Don’t confuse them with hard taco shells, which are folded, or tortilla chips, which are cut into triangles.
Baked shells. Use homemade corn tortillas or bought ones, ideally a day old, since drier tortillas crisp faster. Brush both sides with very little oil and bake in a single layer at 400°F (200°C) for 10 to 12 minutes, flipping halfway. They’re ready when golden and rigid, and they don’t bend when you lift one by the edge. They firm up more as they cool, so if the middle still flexes a bit, give them 2 more minutes. If they puff, press them flat with a spatula when you flip them.
Fried shells. Heat ½ in (1 cm) of oil to 350 to 355°F (175 to 180°C) in a skillet and fry one tortilla at a time, about 1 minute per side, until golden and the bubbling has nearly stopped, which tells you the water has cooked out. Drain them standing on edge on paper towels. Without a thermometer, the tip of a tortilla should bubble hard the moment it touches the oil; weak bubbling means greasy shells.
Cooled homemade shells stay crisp for several days in a sealed bag or tin at room temperature. If they soften, a short spell in the oven, 4 minutes at most, brings them back.
Keeping the shells crisp
- Drain twice. Once when you open the cans, and again just before serving: tomato and lime keep releasing juice in the bowl.
- Put down a barrier. Mashed avocado, a thin layer of mayo or a spoonful of Mexican refried beans on the shell keeps the liquid off the corn and gives the topping something to stick to.
- Build to order. A tostada starts to lose its crunch as soon as the topping goes on. For a sit-down meal, assemble at the table. For a party, set out the chilled mix, the avocado and a stack of shells, and let people build their own.
- Packed lunch. Mix and avocado in one container, shells in a bag, and assemble when you eat. Three shells and about 1 cup (200 g) of mix make one lunch.
When it tastes flat, salty or watery
- Watery → the tuna wasn’t pressed or the tomato wasn’t seeded. Spoon off the liquid before serving.
- Tastes only of tuna → it needs more lime or salt. Taste it on a shell, not off a spoon, because the corn needs a slightly saltier topping.
- Too salty → some brands are heavily salted. Season last and lightly; ¼ tsp for three cans is usually plenty.
- Raw onion takes over → chop it finer, or rinse it under cold water and pat it dry before mixing.
The creamy mayo version, and a warm one
With mayonnaise. For the same three cans, mix the drained tuna with 4 tbsp (60 g / 2 oz) mayonnaise, just 1 tbsp (15 ml) lime juice, and the tomato, onion and cilantro from the recipe. Swap the serrano for 2 pickled jalapeños, chopped, plus 1 tbsp of their brine. Add ½ cup (3 oz / 80 g) drained canned corn or a grated carrot if you like. It comes out creamy and milder, and a serving of 3 tostadas rises to about 425 calories. For something softer still, use 2 tbsp mayo and 2 tbsp Mexican crema or sour cream.
Chipotle mayo. Blend or mash 1 chipotle in adobo into the mayonnaise first, for smoke and medium heat.
Warm atún a la mexicana. Soften the onion in 1 tbsp oil over medium heat for 3 minutes, add the tomato and chile and cook 5 minutes, until the tomato breaks down and there’s no loose juice. Stir in the drained tuna and heat 2 to 3 minutes. Leave out the cucumber and lime, and serve it on tostadas with beans, in tacos or with rice.
Heat level. One serrano with the seeds out is mild; two whole ones are medium. Cooking for kids, leave the chile out and put hot sauce on the table. The mayo version without chile is the one children usually take to.
Feeding a crowd and making ahead
Plan on 2 tostadas a head when there are other dishes and 3 when they’re the meal. Each 5 oz (140 g) can makes about 4 tostadas:
| People | Tostadas | 5 oz cans | Tomatoes | Cucumber | Lime juice |
|---|---|---|---|---|---|
| 4 | 12 | 3 | 7 oz (200 g) | 5 oz (150 g) | ¼ cup (60 ml) |
| 10 | 30 | 8 | 1 lb 2 oz (500 g) | 13 oz (375 g) | ⅔ cup (150 ml) |
| 20 | 60 | 15 | 2¼ lb (1 kg) | 1⅔ lb (750 g) | 1¼ cups (300 ml) |
For 20, buy about 65 shells, because a few always break in the pack, and around 5 avocados. Nearly all the cost is the tuna, and multipacks of chunk light are the cheapest way to buy it.
What you can do ahead. Chop the onion, chile and cilantro up to 4 hours early and keep them covered in the fridge, and drain and flake the tuna too. Leave the tomato and cucumber until last, since they weep. Combine everything no more than 1 to 2 hours ahead, and slice the avocado at serving time.
On the table. Keep the bowl cold, ideally set in a larger bowl of ice, and don’t leave it out of the fridge for more than 2 hours, less on a hot day. The same rule applies to the mayo version.
Storing leftovers. Refrigerated in a sealed container within 2 hours, the mix keeps 3 to 4 days, although the tomato and cucumber soften and weep as the days go by; I eat it within two days and drain it each time. Don’t freeze it: the vegetables and mayo turn watery when thawed. Assembled tostadas don’t keep at all, so store the mix and shells separately.
Frequently asked questions
Is canned tuna safe during pregnancy? It’s cooked, so the raw-fish concern doesn’t apply. The thing to watch is mercury: canned light tuna, made from skipjack, is among the lower-mercury fish and can be eaten 2 to 3 times a week, while white albacore has more and is best kept to once a week. Keep the mix well chilled.
Can I use fresh tuna? Yes, but that’s a different dish: raw tuna diced and cured in lime like a ceviche, and it has to be fish sold for eating raw, bought from a fishmonger you trust and kept very cold. Don’t swap it into this recipe one for one.
What else can I serve it on? Saltine crackers are a common stand-in at home in Mexico; top them right before eating, because they soften faster than tostadas. Lettuce leaves or tortilla chips work too.
Is it gluten-free? Corn tostadas don’t contain wheat, but some brands are made on lines shared with wheat products, so check the label if you’re cooking for someone with celiac disease. The recipe contains fish; the mayo version adds egg, and crema adds milk.
Nutrition
Per serving (a third of the tuna mix and avocado on three store-bought shells), worked out ingredient by ingredient from the quantities above:
- Calories: 325 kcal
- Protein: 18 g
- Carbohydrates: 33 g
- Fat: 15 g, of which 4 g saturated
- Fiber: 6 g
- Sugars: 3 g
- Sodium: 570 mg
More than half of it is the fried shells, about 175 kcal, while the avocado adds roughly 63. On its own, the tuna and vegetable mix gives 15 g of protein for about 87 kcal, which is why the mayo version (about 100 kcal more) or oil-packed tuna (about 80 more) changes the numbers so much.
On a weeknight when the stove stays off, this is my dinner. I keep the shells in a tin and a few cans of tuna in the cupboard, so all I buy fresh is tomato, a cucumber and limes. My son Dylan likes his with mayo and no chile, mine has two serranos, and both come out of the same bowl before the seasoning splits. Press the tuna dry and the rest takes care of itself. Josnaisis.