Cook the lentils and frozen beans in boiling salted water for about 10 minutes. Drain, rinse with cold water and let drain. Wash lemon hot, dry and cut into slices. Heat 1 tablespoon of oil.
Briefly sauté the lemon slices in it.
Clean, wash and cut the spring onions into rings. Wash parsley and shake dry, chop finely. Crumble feta.
Mix lemon juice, mustard, salt and pepper. Fold in the rest of the oil. Mix the prepared ingredients with the dressing.