Place flour in a medium saucepan. Gradually add milk; stir with a whisk until blended. Bring to a boil over medium heat. Cook 6 minutes or until thick; stir constantly. Add pepper and processed cheese; cook 2 minutes or until cheese melts. Stir constantly.
Combine cheese sauce, noodles, onions, and corn in a bowl. Spoon into a 2-quart casserole coated with cooking spray; sprinkle with Parmesan. Bake at 450° for 10 minutes or until bubbly. Broil 3 minutes or until lightly browned.