Beef stir fry with pickled mustard green

Pickled mustard green (hum choi ) is one of my favourite Chinese pickle. It's quite versatile, can be used for soup like this duck soup, braising with meat or stir fries. There are various types; some salty, some with a tangy taste, some sweet and sour, some with leaves, some without (like half a cabbage), some with chilli. I don't use those in a tin for cooking, they are nice with plain rice