Pour the vegetable oil into the wok or pan and heat as hot as possible. While oil is heating, chop steak into bite-size pieces. When oil is hot, carefully put beef into wok and stir-fry until exterior is seared--which should take less than 30 seconds. Remove the beef and keep warm.
Carefully spoon out hot oil and either reserve for further preparations or throw it away.
Put half the soy sauce, the garlic, and ginger into the wok and add all the vegetables. Sprinkle with sherry and stir quickly. Cover to allow vegetables to steam for one minute.
Remove cover, stir vegetables, and return beef to wok.
In a separate bowl, blend remaining soy sauce, oyster sauce, salt, pepper, and cornstarch and pour over contents of wok. Stir fry for 15 seconds over high heat. Serve immediately.