1.In A Small Skillet, Saute Onion In Oil Until Tender. Transfer To A Greased 1-Qt. Baking Dish. Place Fillet Over Onions. Sprinkle With Salt And Pepper. Top With Tomato Slices. Combine Butter And Garlic Powder; Pour Over Tomato. Sprinkle With Parsley. 2.Bake, Uncovered, At 350 Degrees F For 14-18 Minutes Or Until Fish Flakes Easily With A Fork.