01 - In a small bowl, combine kosher salt, black pepper, smoked paprika, garlic powder, onion powder, and ground cumin. Rub this mixture evenly over the beef chuck roast.
02 - Place the thinly sliced onion and minced garlic in the bottom of the slow cooker. Lay the seasoned beef roast on top.
03 - Whisk together beef broth, barbecue sauce, apple cider vinegar, and Worcestershire sauce in a separate bowl. Pour this mixture over the beef in the slow cooker.
04 - Cover and cook on LOW heat for 8 hours, until the beef is very tender and shreds easily with a fork.
05 - Remove the beef from the slow cooker and shred it using two forks. Skim any excess fat from the cooking liquid, then return the shredded beef to the cooker and stir to coat with the juices.
06 - Toast buns if desired. Pile the shredded beef onto the buns, topping with extra barbecue sauce, coleslaw, and pickles as preferred. Serve immediately.