In a bowl mix together all the marinade ingredients then add the flank steak. Set aside for at least 10 minutes. While waiting blanch the broccoli in boiling water for 30 seconds then drain and rinse with cold water.
Combine all the sauce ingredients together in a small bowl. Set aside. Heat cooking oil on high in your wok or non-stick pan for about 2 minutes.
Add beef to the pan and sear until brown. Add the garlic and cook until no longer pink. Pour in the sauce and stir until it thickens. Stir in the broccoli and add salt and pepper to taste.
Top with sesame seeds and green onions and serve over warm rice or noodles.