Heat oven to 400 degrees F. Grease rectangular baking dish, or 3-quart casserole.
Cook and stir in onion in margarine in 3-quart saucepan over medium-low heat until tender. Stir in wine, beans, soup, and mushrooms; heat through. Pour into dish. Top with French fried onions and Fish Fillets.
Bake uncovered until mixture is bubbly and Fillets are hot, 25 - 30 minutes.