01 - Pat beef dry and season with salt, pepper, smoked paprika, cumin, and chili powder.
02 - Heat olive oil in a large skillet over medium-high heat and brown roast on all sides, about 3-4 minutes per side.
03 - Place sliced onions and minced garlic in slow cooker base; lay seared beef on top.
04 - Mix beef broth, barbecue sauce, apple cider vinegar, Worcestershire sauce, and brown sugar; pour over beef.
05 - Cover and cook on low for 8 hours until meat is tender and shreds easily.
06 - Remove beef, shred with two forks, then return to slow cooker and mix with juices.
07 - Whisk mayonnaise, apple cider vinegar, Dijon mustard, honey, celery seed, salt, and pepper in a bowl.
08 - Add shredded cabbage and carrots to dressing; toss well and refrigerate until serving.
09 - Serve pulled beef on buns, drizzle with extra barbecue sauce if desired, then top with slaw.