Classic Ceviche - cooking recipe

Ingredients

1 1 lb halibut fillets or 1 lb other ocean fish fillet, cut into 1/2-inch dice
1 1/2 cups fresh lime juice
1 medium white onion, chopped into 1/2-inch pieces
2 medium tomatoes (about 1 pound) or 2 large tomatoes, chopped into 1/2-inch pieces (about 1 pound)
1 -3 fresh hot green chili pepper, stemmed, seeded and finely chopped (2 to 3 serranos or 1 to 2 jalapenos)
1/3 cup chopped cilantro, plus a few leaves for garnish
1/3 cup chopped pitted green olives (manzanillos for a typical Mexican flavor)
1 -2 tablespoon extra virgin olive oil (optional)
salt
3 tablespoons fresh orange juice or 1/2 teaspoon sugar
2 small avocados, peeled, pitted and diced
tostadas, tortilla chips or saltine crackers, for serving

Preparation

In a 1 1/2-quart glass or stainless steel bowl, combine the fish, lime juice and onion. Use enough juice to cover the fish and allow it to float freely; too little juice means unevenly \"cooked\" fish. Cover and refrigerate for about 4 hours, until a cube of fish no longer looks raw when broken open. Drain in a colander.
In a large bowl, mix together the tomatoes, green chiles, cilantro, olives and optional olive oil. Stir in the fish and season with salt, usually about 1/2 teaspoon. Add the orange juice or sugar. Cover and refrigerate if not serving immediately. Just before serving, gently stir in the diced avocado.
MAKE AHEAD Working ahead: The fish may be marinated a day in advance; after about 4 hours, when the fish is \"cooked,\" drain it so that it will not become too tangy. For the freshest flavor, add the flavorings to the fish no more than a couple of hours before serving.