In a 4- to 6-quart slow cooker, add the onion, bell peppers, and flank steak.

In a small bowl, add the coconut aminos, beef broth, garlic, rice vinegar, sesame oil, ground ginger, sea salt, and black pepper. Pour the sauce over the beef and stir to combine.

Cover and cook on LOW for 7 hours or until meat is cooked through. Serve with cooked cauliflower rice, if desired.