01 - Pat the beef chuck roast dry and season evenly with salt, pepper, smoked paprika, cumin, and chili powder.
02 - Heat olive oil in a large skillet over medium-high heat. Sear the roast on all sides until browned, approximately 3 to 4 minutes per side.
03 - Place sliced onions and minced garlic at the bottom of the slow cooker, then set the seared roast on top.
04 - Combine beef broth, barbecue sauce, apple cider vinegar, Worcestershire sauce, and brown sugar in a bowl. Pour mixture over the beef. Cover and cook on low for 8 hours until beef is very tender.
05 - Remove beef from slow cooker. Shred using two forks and return meat to the pot, mixing with the juices.
06 - In a large bowl, whisk mayonnaise, apple cider vinegar, Dijon mustard, honey, celery seed, salt, and pepper until smooth. Add shredded cabbage and carrots; toss to coat. Refrigerate until serving.
07 - Pile pulled beef onto sandwich buns, drizzle with extra barbecue sauce if desired, and top with prepared slaw. Serve immediately.