Generously season the chuck roast with salt and pepper on all sides and let it rest for about 10 minutes.

In a large skillet, heat olive oil over medium-high heat. Sear the seasoned chuck roast for 3-4 minutes on each side until brown.

Sauté diced onion and minced garlic in the same skillet for about 5 minutes until soft and fragrant.

Add chili powder, cumin, smoked paprika, oregano, and cayenne pepper, cooking for an additional minute.

Transfer the onion and spice mixture into the slow cooker with the beef.

In a medium bowl, whisk together beef broth, tomato paste, lime juice, and soy sauce. Pour over the beef in the slow cooker.

Cover the slow cooker and set to low heat. Cook for 8-10 hours until the beef is tender and shreddable.

Remove the chuck roast and shred with two forks, mixing with the accumulated juices.

Warm the tortillas in a skillet or microwave until pliable.

Fill each tortilla with shredded beef and top with cheese, sour cream, cilantro, tomatoes, and avocado. Serve immediately.