Aguachile Shrimp Ceviche

4 lbs Shrimp - peeled, cleaned and devained, rinse thoroughly
1 large red onion - thinly sliced
4 cups freshly squeezed lemon juice
10 serrano chiles - finely chopped (give or take a few depending on how spicy you want it)
Salt & pepper to taste
Tostadas

Place all ingredients in a bowl making sure there is enough lemon juice to cover the shrimp. Place in the refrigerator for an hour and the shrimp turns pink. Serve over tostada - Enjoy!