1. Pat halibut steaks dry. Arrange fish, thickest parts to outside edges, in rectangular dish, 11 x 7 x 1 1/2 inches. Sprinkle with wine, salt and oregano.
2. Cover tightly and microwave on high 3 minutes; drain. Sprinkle with bread crumbs and cheese; drizzle with margarine. Rotate dish 1/2 turn.
3. Microwave uncovered 3 to 5 minutes or until small ends of fish flake easily with fork. Let stand uncovered 3 minutes. Sprinkle with onion.