1. In a small bowl, combine fish, lime juice, and onion. Be sure the fish is covered with lime juice; add more if necessary. Cover with plastic wrap, and refrigerate until fish no longer looks raw when broken open, about 4 hours. Drain in a colander.

2. In a large bowl, combine tomatoes, jalapenos, cilantro, olives, and oil. Add the fish and orange juice; stir to combine. Season with salt. Cover, and refrigerate if not serving immediately.

3. Just before serving, add avocado, and stir gently, being careful not to break up pieces. Garnish with cilantro leaves, and serve with tortilla chips.