Sounds like something my mom calls Choi Sum. I just call it the chicken rice veggie since chicken rice stalls sell them often. The common way to cook them is to steam or boil them in water until the stalks are tender and leaves are bright green. Then you saute some garlic in hot oil, pour it over the veggies, mix some oyster sauce and water in the same pan, heat it a little and pour it over everything.

One guy has a real novel way of serving them though. He steams them until the stalks are tender, then chills them cold. And serves the veggies up with wasabi and soy sauce for dipping. Its actually quite a tasty way of eating them.