Method:
Cut steak into 1/2-inch-thick slices against the grain and cut slices again into thin strips (don't worry if your pieces are not totally uniform). Place in a bowl and toss with tamari, vinegar and ginger. Cover and refrigerate 20 minutes to overnight.
Remove steak from marinade and discard any extra marinade. Toss steak with cornstarch until evenly coated. Heat oil in a wok or large skillet over high heat. When very hot, but not smoking, add steak and cook until just browned. Remove steak and set aside. Add garlic and asparagus to the wok and stir 1 minute. Add hoisin and 1/2 cup water and stir 1 minute. Return beef to wok, cover, and cook until asparagus is tender, about 4 minutes. Top with green onions and serve.