Marinate the Fish: Place the diced fish in a bowl and cover with lime and lemon juice. Make sure the fish is fully submerged in the juice. Cover and refrigerate for about 2 hours, or until the fish is opaque and fully "cooked" by the citrus juice.
Prepare the Vegetables: In a separate bowl, mix the chopped onion, tomatoes, cucumber, bell pepper, and minced garlic.
Combine Ingredients: After the fish has marinated, drain off some of the citrus juice, leaving a small amount to coat the fish. Add the prepared vegetables to the fish. Mix well.
Season: Add chopped cilantro, salt, pepper, and ketchup or hot sauce if using. Stir to combine.
Enjoy your meal!