Wash the potatoes and cook in boiling water for about 20 minutes, rinse with cold water and peel the skin. Meanwhile clean and wash the beans and cook them in boiling salted water for about 10 minutes, drain, quench cold and let them cool down. Cook the lentils in boiling salted water at medium heat for 5-8 minutes. Drain. Clean, wash and quarter the tomatoes.
Drain mozzarella balls. Clean, wash and quarter the cucumber lengthwise and cut into slices. Drain gherkins and cut into slices. Potatoes, beans. Mix lentils, tomatoes, mozzarella, cucumber and gherkins in a bowl. Wash the chives, dab dry and cut into small rolls. Mix vinegar and mustard. Season with salt and pepper. Whip the oil into the mixture. Stir in chives.
Mix vinegar and mustard. Season with salt and pepper. Whip the oil into the mixture. Stir in chives. Mix marinade and salad ingredients. Leave to stand for about 30 minutes. Season to taste again