01 - Pat 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 roast on all sides until browned, approximately 3-4 minutes per side.
03 - Layer sliced onions and minced garlic at the bottom of the slow cooker, then place seared beef on top.
04 - Whisk together beef broth, barbecue sauce, apple cider vinegar, Worcestershire sauce, and brown sugar; pour mixture over beef. Cover and cook on low for 8 hours until beef is tender and shreds easily.
05 - Remove beef and shred using two forks. Return shredded beef to slow cooker and mix with cooking juices.
06 - In a large bowl, whisk mayonnaise, apple cider vinegar, Dijon mustard, honey, celery seed, salt, and pepper until combined.
07 - Add shredded cabbage and carrots to dressing. Toss well to coat and refrigerate until serving.
08 - Pile shredded beef onto buns, optionally drizzle with extra barbecue sauce, and top with prepared slaw. Serve immediately.