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 and fully combined.
03 - Combine the chili powder, cumin, smoked paprika, oregano, salt, black pepper, and cayenne pepper in a small dish. Pat the chuck roast dry with paper towels, then rub the spice mixture thoroughly over all surfaces of the meat.
04 - Place the seasoned roast directly on top of the onion and garlic bed in the slow cooker.
05 - Pour the broth mixture evenly over the beef and onions.
06 - Cover with the lid and cook on low heat for 8 hours, until the beef is fork-tender and easily pulls apart.
07 - Transfer the cooked roast to a cutting board. Using two forks, shred the meat by pulling in opposite directions. Return the shredded beef to the slow cooker and stir thoroughly to absorb the cooking juices.
08 - Serve hot in taco shells, over rice, in sandwich rolls, or as desired.