Preparation / Directions:
Rinse and pat dry fish fillets. Place fish in 10-inch by 8-inch oven-proof glass or stainless steel baking dish. Combine vinegar, lemon juice, dried mustard powder, and chopped onion in a small mixing bowl. Pour over fillets.
Cover dish and marinate fish in refrigerator for approximately 2 hours.
Preheat broiler. Remove cover from dish and place dish in broiler for approximately 4 to 6 minutes, or until fish is white and flaky throughout.
Garnish with parsley and onion slices.