Cut fish (if needed) into 2, 3 or 4 pieces, using a cutting board dedicated to raw meats/fish. Place fish in the tomato mixture, spooning some of the mixture over the fish. Sprinkle a little more salt and pepper on top. Cover and simmer on low for 7-9 minutes, until fish is opaque and comes apart with a fork. (The cooking time depends on the thickness of the fish. If using thin fish fillets, cook only 2-3 minutes.)