Peel and clean shrimps, remove head and black strip if needed. Cut them along to make butterfly cut or you could cut them completely.
Peel cucumber, cut it in half, remove seeds and cut it in half moons.
Blend lime juice, serrano peppers, coriander, salt and pepper. If you don´t like it too spicy you could remove seeds from serrano pepper before blending it, if you prefer it spicier leave seeds and add more serrano pepper.
Place in a bowl or a plate shrimps, cover them whit lime and serrano pepper, mix and let it sit for 30 minutes in the fridge.
Time passed stir whit cucumber and purple onion.
Add, on top, El Chilerito Hot Spicy Sauce.
Season to taste (is needed) and serve with tostadas.
Note: Shrimps are "cooked" by lime juice, but if you are afraid of eating raw ahrimps, you could cook them first and them make this recipe as explained.