Place the marinade ingredients—light soy sauce, sesame oil, Shaoxing rice wine, and cornstarch into a medium bowl and stir to combine. Set it aside.

Cut the beef into thick slices about 2"/5cm long and place into the bowl of marinade. Cover with plastic wrap and place in the fridge for at least 20 minutes (or overnight) to marinate.

Heat a wok over high heat until very hot, then add the groundnut oil. When the oil is hot and slightly smoking, add the beef and stir fry for 5 minutes until cooked. Remove beef from the wok, drain, and discard oil.

Reheat the wok and add the oyster sauce. Bring to a simmer and add the drained beef slices to the sauce. Stir to mix thoroughly, then transfer to a serving dish.
Garnish with spring onions, serve, and enjoy!