Season roast on all sides with salt, pepper, garlic, cumin, and oregano; place it in a large slow cooker.
Add bell peppers and onion to the slow cooker. In a small bowl, whisk together broth and tomato paste; pour mixture over the beef and vegetables then add the bay leaf.
Cover and cook on LOW for 7 hours or until beef is fork-tender.
Remove roast to a bowl, allow it to cool then shred the cooled beef with your very clean hands.
Return shredded beef to the crock cooker; blend with juices and heat through. Remove bay leaf, fold in olives and serve.