Slice the sirloin steak thinly against the grain and marinate with salt and freshly ground black pepper. Let sit for 10 minutes.

Heat a large wok over high heat until shimmering. Add sunflower oil and sesame oil.

Add the marinated steak to the hot wok in a single layer, searing for 2-3 minutes without stirring.

Remove the beef, stir-fry sliced onions and bell peppers for 3-4 minutes until softened.

In a separate jug, mix cornflour, dark soy sauce, oyster sauce, rice wine, and beef stock.

Add minced garlic and ginger to the vegetables, then pour in the sauce and let simmer for 2-3 minutes.

Add the beef back to the wok, stir-fry for another 2-3 minutes, ensuring the beef is coated in sauce.

Serve immediately, garnished with scallions and sesame seeds over jasmine rice or garlic noodles.