Bring a large pan of salted water to the boil, add a little salt, and then cook the beans for 3-5 minutes, until bright green and tender
Plunge into cold water, then drain.
Heat the frying pan over a medium heat, then add in the butter and garlic. Cook until just starting to colour.
Stir in the beans, and cook until just starting to wilt, no more than 3-4 minutes.
Add the lemon zest to the pan, turn up the heat and add in the juice. Allow to bubble, then transfer to a serving dish. Sprinkle with the chopped parsley.