Cut the beef steak into thin slices. Put the sliced beef into a mixing bowl and add ingredients from beef marinade. Mix well, set aside and marinate at least 15 mins.
Finely chop the garlic. Cut the onion and bell pepper into thin slices.
In a small bowl, mix all the stir fry sauce ingredients. Set aside.
Heat the pan into high heat, add the marinated beef, flatten and spread the beef in the pan. Let it cook the beef for 2-3 mins untill the beef gets a nice charred colour and turn sides. Stir fry for another 1-2 minutes. Remove from the pan and set aside.
In the remaining oil, stir fry the garlic for a few seconds. Then add the onion slices and stir for a few seconds. Add pepper slices, add beef slices back in.
Pour the sauce mixture in. Mix all the ingredients well with the sauce until well combined. Stir fry for about 1-2 mins until the sauce becomes thick and glossy.
Transfer to serving plate. Serve immediately.
Perfect with a bowl of steamed rice or stir fry noodle.