Wash potatoes thoroughly and cook in boiling water for 15-20 minutes. In the meantime, clean and wash the radishes and cut them into slices, except for 4 pieces. Wash and dice the cucumber. Wash and quarter the apple, cut out the core and cut the quarters into thin slices.
Sprinkle with 1 tablespoon of lemon juice. Drain the potatoes, rinse with cold water, peel and quarter the potatoes. Wash the herbs, dab dry and chop finely, except for something to garnish.
Mix yoghurt, herbs, olive oil and mustard. Season to taste with salt, pepper and lemon juice. Mix potatoes, radishes, cucumber, apple and yoghurt marinade and let it soak for some time. Soak the rolls in water.
Peel and finely chop the onion. Squeeze out the bread roll. Knead minced meat, roll, onion and egg to a dough and season with salt and pepper. Heat oil in a pan. Form 8 meatballs with wet hands and fry them while turning for about 8 minutes.
Arrange on plates and serve garnished with herbs and radishes.