Turn under any thin edges of fish. In a 12x7Ωx2-inch baking dish (use an 8x8x2-inch baking dish for low-wattage ovens) arrange thicker portions of fish fillets toward outer edges of the dish. Brush fish with buttermilk or yogurt.
In a small mixing bowl cook margarine on 100% power (high) about 30 seconds or till melted. Stir in stuffing mix, salt, and red pepper.
Spoon stuffing mixture over fish fillets. Cook fish, uncovered, on high for 4 to 7 minutes (7 to 9 minutes for low-wattage ovens) or till fish flakes easily when tested with a fork. Give the dish a half-turn after 3 minutes.