In a nonstick skillet, saute onion and green pepper in butter until tender; remove and set aside. In the same skillet, brown beef over medium heat until no longer pink; drain. Add the tomato sauce, water, seasoning blend, thyme, pepper and vegetables. Cover and simmer for 20-30 minutes or until meat is tender.
Remove from the heat. Sprinkle with cheese; cover and let stand for 5 minutes or until cheese is melted. Serve with spaghetti.