Tan ho, a salad green?
There are actually two kinds of tonghao (as it's called in Mandarin). The one that looks like arugula is called shantonghao (mountain tonghao). You can saute it with garlic. The 'regular' tonghao has rounder leaves.

Both types of tonghao are used in hotpots - you just cook them for a short while and they're done. Similarly, they're used in savory tangyuan soup. Tangyuan are small glutinous rice flour dumplings - some are filled with ground meat, some just plain. The savory soup has tonghao, tangyuan, and shallots.

This is in Taiwan at least - I'm not sure whether people do different things with tonghao in other areas.