Boil the edamame beans in a pan of salted boiling water for 5 minutes. Drain, refresh in a bowl of ice-cold water, then drain again. Pod the beans.
Whisk the mustard, lemon juice and olive oil together in a small bowl. Season with salt and pepper. Taste and add more seasoning, mustard or lemon juice if needed. Gently toss the leaves and beans in just enough of the dressing to coat (you