For the meatballs, soak rolls in water. Peel and finely dice the onion. Squeeze the roll well and knead it with minced meat, diced onion and egg. Season with salt and pepper.
Form 4 flat meatballs from the minced dough with moistened hands. Heat the oil and fry the meatballs for about 5 minutes on each side until crispy. In the meantime, clean and wash the lettuce, cucumber and radishes.
Chop the salad. Cut cucumber and radishes into thin slices. Cut the bread roll in half. Spread the lower halves with remoulade. Alternately cover with lettuce, cucumber, radishes and meatball. Place tartar sauce on top again, sprinkle with roasted onions and place the top of the roll on top.