Cook spaghetti according to package directions, omitting salt and fat.
While spaghetti cooks, cook ground round and onion in a large nonstick skillet over high heat 4 to 5 minutes or until beef is browned, stirring until beef crumbles. Drain beef mixture, if necessary; wipe skillet with paper towels.
Return beef mixture to skillet. Stir in tomato sauce and next 4 ingredients. Cook over medium heat 2 to 4 minutes or until hot and bubbly, stirring occasionally.
Stir in cooked spaghetti and zucchini. Cook 2 minutes, stirring occasionally. Stir in tomato.