1. Arrange fish with thickest parts to outside edge in baking dish, 10x6x2 inches. Sprinkle with wine, salt and oregano. Cover tightly and microwave on high (100%) 3 minutes; drain.
2. Sprinkle fish with bread crumbs and cheese; drizzle with margarine. Rotate baking dish 1/2 turn. Microwave uncovered on high (100%) until small ends of fish flake easily with fork, 2 to 4 minutes. Let stand 3 minutes. (Fish will continue to cook while standing.) Remove fish to platter. Sprinkle with onion.