01 - Arrange the sliced onion and minced garlic evenly across the bottom of the slow cooker insert.
02 - Whisk together the beef broth, tomato paste, and Worcestershire sauce in a small bowl until smooth.
03 - Combine the chili powder, cumin, smoked paprika, oregano, salt, black pepper, and cayenne pepper in a small bowl.
04 - Rub the spice mixture thoroughly over all surfaces of the chuck roast, pressing gently to adhere.
05 - Place the seasoned roast on top of the onion and garlic bed in the slow cooker.
06 - Pour the broth mixture evenly over the beef and aromatics.
07 - Cover and cook on low heat for 8 hours until the beef is fork-tender and easily shreds apart.
08 - Transfer the cooked beef to a cutting board and shred using two forks. Return the shredded meat to the slow cooker and toss with the cooking juices.
09 - Serve hot with your choice of tortillas, bread, or over rice.