Coat a 3-quart rectangular baking dish with nonstick cooking spray; set aside. Preheat oven to 350°F.
Cook noodles according to package directions; drain. Rinse with cold water; drain again.
Meanwhile, coat an unheated large skillet with nonstick cooking spray. Preheat over medium heat. Add chicken to hot skillet. Cook and stir about 3 minutes or until chicken is no longer pink. Transfer chicken to a large bowl.
Add mushrooms, green onions, and sweet pepper to skillet. Cook and stir until vegetables are tender. (If necessary, add 1 tablespoon vegetable oil to skillet.)
Transfer vegetables to bowl with chicken. Stir in cream of broccoli soup, sour cream, broth, mustard, and black pepper. Gently stir in cooked noodles and broccoli.
Spoon chicken mixture into prepared dish. In a small bowl combine bread crumbs and melted butter; sprinkle over chicken mixture. Bake, covered, for 30 minutes. Uncover and bake about 25 minutes more or until heated through.