Freeze beef 15 minutes then thinly slice. Toss the sliced steak with cornstarch and about1 tablespoon of Shaoxing or sherry. Marinate 15 minutes.
Heat a stir-fry or round-bottom pan over high heat with stir-fry oil. Add beef and brown well; transfer to a plate. Add peppers, onions, garlic, ground pepper and cumin, and stir-fry 2-3 minutes more. Add Worcestershire, sugar, remaining shot of Shaoxing sherry, soy sauce, Sa Cha or Hoisin, and toss to combine. Add the beef back to the pan, toss quickly then remove pan from heat and toss in the scallions. Serve over brown rice.