Marinate the beef slices with the seasonings for 30 minutes. 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.
Heat up another 1 tablespoon of oil and saute the garlic and ginger until aromatic. Add the beef back into the wok and then the sauce. Continue to stir-fry until the beef slices are almost done, then add the leeks into the wok. Do a few quick stirs, add salt and sugar to taste, dish out and garnish with the shredded scallions.