Season and Sear the Beef: Generously season the beef chuck roast with salt and black pepper. In a large skillet, heat olive oil over medium-high heat. Sear the beef on all sides until browned, about 2-3 minutes per side. Transfer to the slow cooker.

Add Remaining Ingredients: Add the chopped onion, minced garlic, diced tomatoes, beef broth, lime juice, chili powder, cumin, smoked paprika, oregano, and cayenne pepper (if using) to the slow cooker. Add the bay leaves.

Slow Cook: Cover and cook on low for 8 hours or on high for 4-5 hours, until the beef is tender and can be easily shredded with a fork.

Shred the Beef: Once cooked, remove the beef from the slow cooker and shred it using two forks. Discard any large pieces of fat. Return the shredded beef to the slow cooker and stir it into the juices.

Serve: Serve the shredded beef with tortillas, rice, or over a salad. Garnish with fresh cilantro if desired.