Steam the beans over a pan of boiling water for 5 mins or cook for 3 mins in a large pan of boiling salted water over a medium heat. Once cooked, plunge into ice-cold water, leave for 2 mins, then drain and leave to dry.

Meanwhile, combine the mustard, vinegar, olive oil, lemon zest and juice, and the garlic. Toss the beans and the dressing together in a large bowl. Serve on a platter with the parmesan sprinkled over.