Cut flank steak into thin strips, and combine with cornstarch in a Ziploc bag. Shake to coat

Add sesame oil, minced garlic, soy sauce, beef broth, brown sugar, onion, and red pepper flakes to slow cooker. Stir ingredients. Add coated flank steak and stir again until coated in sauce.

Cool for 2–3 hours on high or 4–5 hours on low, until cooked throughout and tender.

Serve over rice and garnish with green onions and sesame seeds.