1. Fold fillets in half and arrange in a small, shallow baking dish, with thicker portions toward the outside of the dish. Pour wine over fish. Dot with butter and sprinkle on chopped onion, salt, and pepper. Cover.
2. Microwave at Cook Cycle 1 (power level 10) for 5 to 7 1/2 minutes, or until fish flakes easily with a fork. Let stand, covered, 3 to 5 minutes, or until fish becomes white and firm all the way through.