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 the tomato paste is fully dissolved and incorporated.
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 aromatics.
06 - Cover with the lid and cook on low heat for 8 hours, or until the beef shreds effortlessly when pressed with a fork.
07 - Transfer the cooked beef to a large cutting board. Using two forks, pull the meat apart into shreds. Return the shredded beef to the slow cooker and toss thoroughly with the accumulated cooking juices.
08 - Serve immediately while hot, or keep warm on the low setting until ready to serve.