Place the lemon zest and olive oil in a small bowl and set aside.
Cook the beans, from frozen, in lightly salted boiling water for 5 minutes.
Drain and rinse under cold running water to stop them cooking any more.
Let them cool a little and peel them by popping them out of their skins.
Place the beans and mint in your serving bowl.
Whisk a tablespoon of lemon juice into the lemony oil, along with salt and pepper, adjust to taste, then pour over, giving a gentle toss to dress.
Finish with a crumbling of feta.
