Peel and clean the shrimp. Slice them in half lengthwise and remove the vein. Rinse and set aside.

Squeeze the limes over the shrimp and let them marinate for a few minutes, stirring occasionally so they cook evenly in the lime juice.

Meanwhile, peel the cucumbers, remove the seeds, and cut into small cubes.

Thinly slice the red onion and add to the shrimp once they are opaque and cooked through.

Add a pinch of salt and pepper.

Dice the tomatoes, using only the flesh and discarding the seeds.

Drain the ceviche in a colander and drizzle with about 1 tablespoon olive oil.

Serve on a tostada shell spread with mayonnaise. Top with avocado slices and hot sauce to taste.

You can also add chopped cilantro if you like.