Brush a little oil over the steaks and season the steaks with salt and pepper. Heat a non-stick frying pan until very hot.
Cook the steaks, two at a time, for about 2 minutes on each side, depending on how thick they are. Remove from the pan and keep warm.
Heat a little oil to the pan then add the mushrooms and cook for 1-2 minutes.
Combine the sweet chilli sauce, dark soy, sesame oil and water in a small bowl, stir and add to the pan with the mushrooms.
Allow to cook for 4-5 minutes until the sauce has reduced and is beginning to get sticky. Taste and season.
While the sauce is reducing heat a little oil in a large frying pan or wok. Add the pak choi, red onion and chilli and stir-fry for a couple of minutes until the pak choi has wilted. Stir through the sesame oil and soy sauce. Taste and season.
Place the steaks on serving plates. Spoon the sauce over the steaks.
Serving Suggestions
Serve with the mushrooms, pak choi and some sautéed potatoes.