Heat oven to 350°F. Spray 8-inch square 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 10-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 5 minutes longer or until cheese is melted and casserole is bubbly.