Season the beef with salt and black pepper to taste. In a large skillet, heat the avocado oil. Add the beef cubes and brown on all sides. Transfer the browned beef to a 4- to 6-quart slow cooker.

Add the onion, tomatoes, tomato paste, cumin, and chile powder, if using. Pour the beef stock over the beef and vegetables. For a thicker stew, add the arrowroot powder, if desired. Cover and cook on LOW for 6 to 8 hours, or until beef is cooked through and tender.

Garnish with the cheddar cheese, avocado, cilantro, and lime wedges.