Usually I'm a 'more is more' kind of guy, but today I decided to cook some mustard in a simple manner since it's starting to bolt on me. A couple handfulls of leaves chopped into 1" strips and 3 coarsely chopped garlic cloves stir-fried in a tablespoon of olive oil until it's al-dente (the leaves wilt but the stems are still crispy inside), then a sprinkle of salt on the plate. Takes about 1 minute to cook and it's mmm-mmm good - I went back for 3rds.
I think you could do this with any kind of green, it worked well with hon-tsai-tai too though the hon-tsai-tai was tough from the hot weather compared to the mustard. I was shooting for something like the Chinese broccoli you get in a dim-sum place, and it's in the ball-park. Don't know what the sauce they put on the broccoli is though.