01 - Arrange 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 combined.
03 - Combine the chili powder, cumin, smoked paprika, oregano, salt, black pepper, and cayenne pepper in a small bowl. Pat the chuck roast dry with paper towels, then rub the spice mixture thoroughly over all surfaces of the meat.
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 and vegetables.
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 large cutting board. Using two forks, shred the meat against the grain. Return the shredded beef to the slow cooker and toss thoroughly with the accumulated juices.
08 - Serve immediately in taco shells, on sandwich rolls, or over rice bowls.