In a nonstick skillet, cook the beef, garlic, 1/4 teaspoon salt and pepper in 1 teaspoon oil over medium heat until meat is no longer pink; drain. Remove and keep warm. In the same skillet, saute onion in remaining oil for 2 minutes. Add zucchini and green pepper; cook and stir for 4-6 minutes or until vegetables are crisp-tender.
Stir in the tomatoes, vinegar, basil, thyme and remaining salt. Add the beef mixture; heat through. Serve over the spaghetti if desired.