Place beef in slow cooker, add tomatoes and barbecue sauce. Cover and cook on Low 8 to 10 hours or High 4 to 6 hours or until beef is very tender.
Remove beef from slow cooker and shred using 2 forks. Skim fat from juices then return beef to slow cooker.
Serve beef on buns and top with shredded cabbage or cole slaw if desired. Also tastes great in tortillas or over rice or polenta.
Tip: If you're following a keto diet, use your favorite Keto friendly barbecue sauce.