Brown ground beef together with onions in nonstick skillet over medium heat, stirring frequently, until beef is browned. Drain thoroughly. Mix all ingredients except tortellini and cheese in a 4 to 5 quart crockpot.
Cover and cook on LOW for 8 hours. Add tortellini, stir to combine then sprinkle with cheese. Cover crockpot and cook on LOW for 15-20 minutes or until tortellini is tender and cheese is melted.