Cut the chuck roast into approximately 2-inch pieces, trimming away any large pieces of excess fat as you go.
Place the beef pieces into the slow cooker. Add the diced yellow onion, chipotle peppers, minced garlic, lime juice, apple cider vinegar, cumin, oregano, salt, black pepper, and beef broth. Stir everything together so the beef is well coated in the seasonings and cooking liquid.
Cover and cook on LOW for 8–9 hours or HIGH for 4–5 hours, until the beef is incredibly tender and easily pulls apart with a fork.For the most tender, flavorful barbacoa, I prefer cooking the beef low and slow when time allows. Carefully transfer the cooked beef to a cutting board.
Using two forks, shred the beef into bite-sized pieces. Discard any large pieces of excess fat as you shred.
Return the shredded beef to the slow cooker and stir it into all of those flavorful cooking juices.
Let the shredded beef sit in the juices for a few minutes before serving so it can soak up even more flavor.
Pile the barbacoa beef into warm tortillas and top with diced red onion, fresh cilantro, and a squeeze of lime juice.Or skip the tortillas and serve the beef over rice for an easy barbacoa bowl.Enjoy!