In 4-quart Dutch oven, cook beef and 1 1/2 cups of the onions over medium heat 8 to 10 minutes, stirring occassionally, until beef is throughly cooked and onions are tender; drain.
Stir in tomatoes, beans, tomato sauce and chili powder, breaking up tomatoes. Cook uncovered over medium heat about 10 minutes, stirring occasionally, until desired consistency. Meanwhile, cook and drain spaghetti as directed on package.
Cover and refrigerate half of chili for another meal. Serve remaining chili over hot spaghetti; sprinkle with cheese and remaining1/2 cup onion.