01 - Layer the sliced onions 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 and fully incorporated.
03 - Combine the chili powder, cumin, smoked paprika, oregano, salt, black pepper, and cayenne pepper in a small dish. Rub the spice mixture thoroughly over all surfaces of the chuck roast, pressing gently to adhere.
04 - Place the seasoned chuck roast directly on top of the onion and garlic bed in the slow cooker.
05 - Pour the broth mixture evenly over the beef, ensuring some liquid flows around the sides of the roast.
06 - Cover with the lid and cook on low setting for 8 hours until the beef is fork-tender and easily pulls apart.
07 - Transfer the cooked roast to a cutting board. Use two forks to shred the meat, pulling it apart against the grain. Return the shredded beef to the slow cooker and toss with the cooking juices.
08 - Serve hot in tortillas, over rice, on sandwich rolls, or as desired.