Trim excess fat from the 3 lbs chuck roast to prevent greasy barbacoa.

Rub 1 teaspoon salt, 1 teaspoon black pepper, 2 teaspoons ground cumin, 2 teaspoons dried oregano, and 1 tablespoon chili powder all over the meat to season thoroughly.

Heat 1 tablespoon olive oil in a searing pan over medium-high heat and sear the meat on all sides, about 2-3 minutes per side, until browned.

Add 4 cloves minced garlic and 1 chopped onion to the pan and sauté for 2-3 minutes until fragrant.

Transfer the meat and aromatics to the slow cooker and add 1/2 cup beef broth, 2 tablespoons lime juice, and 1-2 chipotle peppers in adobo sauce.

Cover and cook on low for 8 hours (480 minutes) until the beef is tender and shreddable.

Remove the meat from the cooking liquid and shred using two forks, then return the shredded beef to the slow cooker to soak up the juices.

Serve the barbacoa warm in tacos, burritos, or over rice, garnished with cilantro and onions as desired.