In 10-inch skillet, cook ground beef and onion over medium heat 8 to 10 minutes, stirring frequently, until beef is thoroughly cooked; drain. Into 3 1/2- to 4-quart slow cooker, spoon ground beef.
In same skillet, cook bacon over medium heat, stirring frequently, until bacon is brown and crisp; do not drain off drippings. Add tomatoes; heat to boiling. With spoon, break up large pieces of tomato. Spoon bacon mixture into slow cooker. Stir in baked beans.
Cover; cook on Low heat setting 4 to 5 hours.