In a large nonstick skillet, cook the beef, mushrooms, and the onion until the meat is no longer pink; drain. Transfer to a 3-qt. slow cooker.
Stir in the tomatoes, tomato paste, tomato sauce, broth, parsley, brown sugar, basil, oregano, salt and pepper. Cover and cook on low 6 - 8 hours. Serve with spaghetti. Sprinkle with cheese if desired.