Cut the beef into thin, bite size pieces, against the grain.
Combine marinade ingredients in a dish and add beef. Let marinade for at least 30 minutes and up to 2 hours.
Mix sauce ingredients in a bowl and set aside.
Heat half the cooking oil over high heat until it just starts to smoke.
Drain any excess marinade from beef and lightly dust with cornstarch.
Cook the beef in two or more batches (to prevent lowering the heat of the wok pan) for about 1-2 minutes, or until juices run clear. Remove beef with a slotted spoon and set aside.
Repeat with second half of oil and second batch.
Add onions and stir fry until translucent, about 1 minute.
Add garlic and ginger and stir fry for about 30 seconds.
Add the green onions and beef (reserving some green onions for the garnish).
Add the sauce mixture and cook for about 2 minutes, or until sauce has thickened.
Garnish with green onions and serve over white rice or crispy noodles.