In frying pan, cook chicken, onion, green pepper, salt and pepper in butter. In separate pan, cook macaroni; just before macaroni is cooked, add frozen broccoli and bring to a boil. Cook 4-5 min. Meanwhile, add soup and milk to chicken mixture. Heat for 15 min. over medium heat. Add to that 1 cup cheese; stir until thick. Strain the macaroni and broccoli mixture. Mix everything together in a 9x13-inch casserole dish and cover with remaining cheese. Cover and bake at 350°F for 30 min., or until cheese is melted.