In 10-inch nonstick skillet, cook beef and onion over medium-high heat 5 to 7 minutes, stirring occasionally, until beef is thoroughly cooked; drain.
Stir in barbecue sauce and chili beans. Heat to boiling. Reduce heat to low; simmer uncovered 10 to 15 minutes, stirring occasionally, until slightly thickened.
Spoon mixture onto bottoms of buns; sprinkle with cheese. Top with tops of buns.