Whisk the oil and oyster sauce with 1 tbsp water in a saucepan. Cook for 2-3 mins until glossy, then set aside.
Bring a large pan of salted water to the boil. Add the greens, turn down the heat and cook for 2 mins, or until just wilted, then drain.
To serve: cut any large bulbs in half and put on a plate. Drizzle the sauce over and serve immediately.