Add some oil to a hot wok or heavy skillet. Lightly coat the beef strips in cornstarch and shake to remove excess. Stir-fry beef until caramelized on both sides. Remove the meat from the wok and set aside. Discard all but 2 teaspoons of the oil.
To make sauce: Add the ginger and garlic to the wok and stir-fry for about 30 seconds. Add remaining sauce ingredients, except for the green onions. Let the sauce simmer for 2 minutes, until sauce begins to thicken.
Return beef to the sauce and stir to coat. Add the green onions and stir again to coat. Simmer for 1 minute seconds. Serve immediately with steamed rice and/or crispy fried cellophane noodles.