Meanwhile, heat oven to 350°F. Spray 12x8-inch (2-quart) glass baking dish with nonstick cooking spray. Melt 1/4 cup margarine in medium saucepan over medium-high heat. Add flour; cook and stir until well blended. Gradually add half-and-half, cooking until mixture boils and thickens, stirring constantly. Stir in seasoned salt and pepper.