Heat olive oil in a large saucepan. Add onion and garlic. Cook until tender but not browned. Add tomatoes, olives, capers, bay leaves, peppercorns and salt to taste. Bring to a boil; reduce heat. Simmer gently uncovered 10 minutes. Place fish fillets in a large skillet and sprinkle with salt. Pour sauce over fish. Bring to a boil; reduce heat. Cover and simmer 10 minutes or until fish flakes easily when tested with a fork.