Ceviche is a Central and South American coastal staple. Seafood is "cooked" in a highly acidic juice, ideally from a citrus fruit to lend the acidity as well as a pleasant flavor. This acidic bath inhibits microbacterial growth and slowly denatures the proteins in the seafood which firms it, making it textured like it was perfectly cooked.
Here is my recipe:
12-15 limes juiced -enough to cover
The zest of 1 line.
2 lbs of shrimp cut into 1/2" cubes
1 lb of Bay scallops
1 red bell pepper diced
1 red onion quartered and thinly sliced
handful of diced Cilantro
salt and pepper to taste
3 Avocados to garnish
Add the Shrimp and Scallops to a bowl and cover with lime juice and lime zest. Toss a few times to make sure every piece is exposed to the juice and store in the refrigerator for 3-4 hours.
Once it's fully "cooked" in the lime juice you could toss it with the vegetables then drain off the juice, this can be drank in shots called Tiger's milk.
However, since mine was going to sit on an open table for 3-4 hours during the party I decided to keep everything in the juice to inhibit the growth of anything nasty.
I had avocados on hand to slice over each taco as they were being assembled. The smooth, rich, creamy texture of avocado makes the perfect counterpoint to the firm tangy ceviche.
You can easily replace the seafood with any other type of ocean fish. Also changing some of the lime juice for other citrus fruits can lend more dimensions. Grapefruit, orange, lemon, all are great substitutions. Tomato sauce is often added in Ecuador.