Mix quark, yoghurt, sugar and lemon juice. Pour mandarin oranges into a sieve. Clean the chicory, loosen the outer 6 leaves. Halve the remaining chicory and cut into strips.
Fold mandarins, except for 6 pieces, and chicory strips into the curd mixture. Place 3 lettuce leaves on top of each other and fill with the quark mixture. Arrange on a plate and garnish with mandarin fillets and sesame seeds.
Cut the buns into slices and add them.