Rub the shoulder steak on all sides with sea salt and black pepper. Place the roast in a 6-quart slow cooker.
In a bowl, add the beef stock, balsamic vinegar, coconut aminos, monk fruit sweetener, and garlic. Pour the mixture over the steak. Sprinkle the red pepper flakes over the beef, if using. Cover and cook on LOW for 8 hours.
Transfer the beef to a cutting board and with 2 forks or a shredder, shred the beef.
Serve the shredded beef over the cauliflower rice or mash.