This salad leaf of the plant Eruca sativa is one of my absolute favorites (as it has been for the Romans and many other cultures). It has the perfectly good English name of “rocket”—why not use it?
One finds it everywhere, with many different levels of quality and taste. The rule of thumb is that smaller leaves are better, although “baby” ones from some varieties can have no taste beyond a slightly soapy one. So taste before buying, and by all means grow your own. Dump a packet of seeds on the ground and up the rocket will come, seeding itself and coming back each year. If put in rich soil and watered, it will keep its milder personality.