Place the beef chuck roast in the slow cooker along with the chopped onion, minced garlic, chipotle peppers, beef broth, 2 tablespoons of the lime juice, cumin, oregano, salt, and black pepper.
Cover and cook on low for 8 hours until the beef is fork-tender and easy to shred.
Shred the beef directly in the slow cooker using two forks and stir it into the cooking juices.
In a mixing bowl, stir together the shredded cabbage, chopped cilantro, mayonnaise, and the remaining 2 tablespoons of lime juice to form the slaw.
Warm the corn tortillas and fill each one with a portion of the shredded beef. Finish with a scoop of the cilantro lime slaw.