01 - Combine kosher salt, black pepper, smoked paprika, garlic powder, onion powder, and ground cumin in a small bowl. Rub evenly over the beef chuck roast.
02 - Place sliced onion and minced garlic in the base of the slow cooker, forming a bed for the beef.
03 - Set the seasoned beef roast atop the onion and garlic. In a separate bowl, whisk together beef broth, barbecue sauce, apple cider vinegar, and Worcestershire sauce; pour evenly over the beef.
04 - Cover and cook on LOW for 8 hours until the beef is tender and shreds easily.
05 - Remove beef from the slow cooker and shred using two forks. Skim excess fat from the cooking liquid, return shredded beef to the cooker, and stir to coat with juices.
06 - Toast sandwich buns if desired. Pile pulled beef onto buns and top with additional barbecue sauce, coleslaw, and pickles as preferred. Serve warm.