– Gently mix tomato, onion, Serrano pepper, and cilantro in a medium-size bowl. I say gently because if you over mix it, it will become a salsa, and this is more like a salad where you enjoy every bite of the ingredients in your mouth.
– Drain any excess liquid from the tuna. Carefully, with the help of two forks, stir the tuna into the rest of the ingredients in the bowl. Add the juice of half a lime, and season with salt and pepper.
– In another bowl, mash the avocado to form a puree, and add a few drops of lime while mashing it. Season with salt and pepper.
– To form the tostadas, spread a portion of the avocado puree over each tostada and top it with the tuna ceviche. To garnish, you can add a few slices of Serrano pepper. Enjoy!