Preheat oven to 375°F. Melt butter in medium skillet on medium heat. Add onion; cook and stir 2 minutes or until softened. Stir in tomatoes, Seafood Sauce and garlic. Reduce heat to low; simmer 3 minutes, stirring occasionally.
Place fish in single layer in lightly greased baking dish. Spoon tomato mixture over fish.
Bake 15 minutes or until fish flakes easily with a fork.