Preheat oven to 375°F. Melt 1 tbsp butter in medium skillet on medium heat. Add 1/3 cup finely chopped onion; cook and stir 2 minutes or until softened. Stir in 1 cup finely chopped seeded tomatoes, 1/4 cup McCormick® Cajun Style Seafood Sauce and 1/2 tsp minced garlic. Reduce heat to low; simmer 3 minutes, stirring occasionally. Place 1 1/2 pounds rockfish fillets in single layer in lightly greased baking dish. Spoon tomato mixture over fish. Bake 15 minutes or until fish flakes easily with a fork. There will be plenty of delicious, saucy broth at the bottom of the pan, so we recommend serving on top orzo or rice to soak it all up.