Cook noodles according to package directions; drain. Meanwhile, in a nonstick skillet, cook the beef, onion and green pepper over medium heat until meat is no longer pink; drain. , In a large bowl, combine the soup, cheese, mushrooms, pimientos, butter, thyme and salt. Stir in the noodles and beef mixture., Transfer to a 2-qt. baking dish coated with cooking spray. Cover and bake at 350° for 25-30 minutes or until heated through.