Heat a little of the oil in a wok and toast the cashew nuts until they start to turn golden. Tip out of the pan, then add the rest of the oil. Stir-fry the broccoli for 2-3 mins until it has turned bright green (it will still be very firm).
Add a splash of water to the pan, then cover with a lid and steam for about 4 mins or until the stems just give with a knife. Push to the side of the pan, then pour the oyster sauce into the other side. Bring to the boil, then stir into the broccoli. Toss in the cashews and serve.