In a large non-stick skillet, cook the meat, onions, mushrooms, green pepper and garlic over medium heat till meat is no longer pink; drain.
Transfer to a slow cooker. Stir in tomatoes, tomato paste, tomato sauce, ketchup, broth, worcestershire sauce, brown sugar, cumin and chili powder. Mix well. Cover and cook on low for 4-5 hours. Serve over spaghetti.