Preheat oven to 350 degrees. Coat the bottom of a baking dish with the olive oil. Sprinkle ¼ chopped onion and 1 garlic clove, minced evenly in the baking dish, and cover with 8 oz pasta sauce. Place 1 lb of haddock fillets in the dish, top with 1 (14 ounce) can stewed tomatoes, drained and ¼ chopped onion and 1 garlic clove minced. Cover with 8 oz pasta sauce. Bake 20 minutes in the preheated oven. Top with ¾ c. mozzarella cheese, and continue baking 10 minutes, until cheese is melted and fish is easily flaked with a fork.