Does anyone know where to find "haam choy" side dish?

I'm not so familiar with it but I was at a friend's house and her mom had it as a side dish and I'm craving that flavor for some reason…but I am not sure where I can find it. It's Chinese, I think.

It translates to pickled mustard greens and it was served with grounded bits of pork. I'm looking for a restaurant that serves it but no Chinese restaurant menu I'm looking at has this. Maybe it's called something else? Thank you for your help!