Heat the avocado oil in a skillet over medium heat. Brown the beef strips in batches for 2 to 3 minutes per side, then transfer them to the slow cooker.
Add the garlic, ginger, fish sauce, coconut aminos, chili flakes, and beef broth to the slow cooker. Stir to combine with the beef.
Cover and cook on low for 5 hours.
Add the green beans and shredded cabbage to the slow cooker. Stir gently, then cover and cook for 1 more hour until the vegetables are tender but still hold some texture.
Turn off the heat and stir in the Thai basil leaves until they wilt slightly.