Preheat oven to 400 F. To make bread crumbs, toast bread to remove moisture. Place toasted bread in a blender or food processor and pulse until it becomes a coarse mixture. Brush fillets with melted margarine to coat all sides. Combine bread crumbs, onion powder, basil and salt. Dredge fish fillets in crumb mixture. Place coated fillets in an 8" x 8" baking dish. Squeeze lemon juice over fish. Bake for 10-15 minutes or until fish flakes when tested with a fork.