Put the beans in a skillet or dutch oven large enough to hold them without crowding.
Cover them with water and add some salt.
Bring to a boil over high heat and cook the beans for 3 to 5 minutes until they are crisp tender.
Drain and run cold water over them to cool them down.
Put the beans in a large bowl and dress with the olive oil, lemon juice, half the mint, salt and pepper.
Toss with half the walnuts and feta cheese.
Transfer to a platter and top with the remaining mint, feta and walnuts