Cut edges off green beans and wash well.
Parboil green beans and transfer to icy water.
Drain well.
Cook and toss on high heat with olive oil and a touch of butter for about 6 minutes.
Add sliced garlic and toss quickly.
Add lemon, salt and black pepper still on high heat and toss one last time.
Turn heat off.
Sprinkle lemon zest on warm green beans.
Serve warm.