Prepare the beef: Pat the chuck roast dry and season lightly with salt and pepper.
Optional sear for flavor: Heat a skillet over medium-high heat and sear the beef on all sides until browned. Transfer to the crockpot.
Build the flavor base: Add chopped onion and garlic over the beef. Pour in beef broth, vinegar, and tomato paste.
Season and cook: Sprinkle cumin, oregano, paprika, and add the bay leaf. Cover and cook on LOW for 8 hours until fork-tender.
Shred and rest: Remove the beef, shred with forks, then return it to the crockpot. Let it rest in the juices for 10 minutes before serving.