The best fish to use are fresh flounder, red snapper or redfish. Cut fish into bite-sized pieces. Place in a shallow dish and add enough lime juice to cover thoroughly. Let marinade for at least 1 hour (longer is better).

Chopped onion
Chopped tomatoes
Chopped fresh serrano or jalapeno peppers
Fresh cilantro leaves (coriander with no stems)
Fresh diced garlic
Salt to taste

Serve as an appetizer with Tostados.