In 3 1/2- to 4-quart slow cooker, mix onion and bacon. Top with beef. Pour barbecue sauce over beef.
Cover; cook on Low heat setting 8 to 10 hours.
Remove beef from cooker; place on cutting board. Cut beef into 1/2-inch pieces. Pour juices from cooker through strainer into small bowl, reserving onion, bacon and 1/2 cup juices. Return beef, onion, bacon and 1/2 cup juices to cooker. Stir in baked beans. Increase heat setting to High. Cover; cook 40 to 50 minutes or until thoroughly heated.