Prepare the Beef: Season the beef chunks with salt, black pepper, cumin, and oregano.
Sauté Aromatics: In a large skillet, heat some oil over medium-high heat. Add the chopped onion and garlic, and cook until fragrant.
Slow Cook: Transfer the beef mixture to a slow cooker. Add chipotle peppers, apple cider vinegar, bay leaves, and beef broth. Cover and cook on low for 8 hours or until the beef is tender and easily shreds.
Shred the Beef: Once cooked, remove the beef from the slow cooker and shred it using two forks. Return the shredded beef to the slow cooker to soak up the remaining juices.
Warm the Tortillas: In a skillet, lightly toast the corn tortillas until warm and pliable.
Assemble Tacos: Fill each tortilla with a generous amount of barbacoa beef, then top with chopped cilantro and diced onions. Serve with lime wedges on the side.