Heat oven to 350°F. Spray 11x7-inch (2-quart) glass baking dish with cooking spray. Cook and drain noodles as directed on package.
Meanwhile, remove fat from beef. Cut beef into 3/4-inch pieces. Heat 12-inch nonstick skillet over medium heat. Cook beef and pepper in skillet 2 to 3 minutes, stirring occasionally, until beef is brown. Stir in onions and bell pepper. Cook 2 minutes, stirring occasionally. Spoon into baking dish.
In medium bowl, beat broth and flour with wire whisk until smooth. Add to skillet; heat to boiling. Cook, stirring constantly, until mixture thickens; remove from heat. Stir in half-and-half and mustard. Spoon over beef mixture. Stir in cooked noodles.
Cover and bake 40 minutes. Sprinkle with cheese. Bake uncovered about 10 minutes longer or until cheese is melted and casserole is bubbly.