Thaw fish, if frozen. Rinse fish and pat dry with paper towels. Cut fish into 4 serving-size pieces, if necessary. Arrange in a 2-quart square baking dish.
In a small saucepan cook onion and garlic in hot butter over medium heat until tender; remove from heat. Stir in parsley, orange peel, salt, and pepper; spoon over fish. Drizzle orange and lemon juice over fish. Bake, covered, in a 400 degree F oven for 15 to 20 minutes or until fish flakes easily with a fork. Spoon pan juices over fish. Makes 4 servings.