Rocket is the best

If you can manage to grow rocket (arugula) successfully, treat them well and you'll get to harvest the leaves for a long time.

The plants I have are already many months old and they're still going strong. New leaves will grow as you cut the old ones. In fact, I tend to forget to harvest them until the leaves are so big and peppery.

I like to add them to my pizza for that extra kick.Needless to say, they are great in salads too.