I've known this plant for as long as I can remember, on account of its cute heart-shaped seed pods.
Seeing it coming up all over my legume bed (it's doing rather better than the peas and beans, if I'm honest), I was struck by its similarity to brassicas. Looking it up, I found that it is indeed a brassica, and all parts of the plant are edible. Apparently the young leaves are very good in early spring, but I've missed the season for those as they're not so good once the plant has flowered. Some people use the seeds, either as they are or ground into meal, but I suspect the only people who do that are those who have small children to employ in the harvesting of said seeds. The seed pods have a peppery taste and can be used as seasoning.
I picked one and tried it and sure enough, it had a distinct peppery bite. Harvesting even the pods turns out to be quite fiddly as they're so small and the stalks are wiry and tend to come off the plant with the pod, so need trimming off afterwards (or more careful picking in the first place). I have to admit, when I cooked a handful of these in a stew, I didn't notice the flavour, but then I wouldn't particularly notice pepper if I'd added it to stew. I'll persevere with this plant; I think it's probably one worth knowing about.
Also harvesting this week
Pak choi flower shoots
Plantain flower heads
Dried (and rehydrated) kelp
Foraged food challenge summary page here.