1. Melt the margarine; add the flour. Whisk and heat a couple of minutes. Gradually add milk, stirring, to make a white sauce. Add cheese; stir until melted.
2. Add remaining ingredients; mix well.
3. Pour into a 2-quart casserole. Cover and bake at 350 degrees F. for 1 hour. Uncover; continue baking 30 minutes longer.