Marinate the beef slices with all the ingredients in Marinade for 10 minutes. In a small bowl, mix all the ingredients in the Sauce, stir to combine well. Set aside.

Heat up a wok with 1 tablespoon of oil and stir-fry the marinated beef until they are half-done. Dish out and set aside. Drain the bloody water from the beef.

Heat up the remaining oil and stir-fry the garlic and onion until aromatic. Add the beef back into the wok and do a few quick stirs before adding the Sauce. Continue to stir-fry until the beef slices are completely cooked, then add the scallions into the wok. Do a few quick stirs, dish out and serve hot with steamed rice.