Mix the yogurt, mayonnaise, dill and a squeeze of lemon with the pressed or finely chopped clove of garlic. Season with a pinch of salt, pepper and sugar, then chill for 30 minutes. Cut the lettuce leaf into fine strips.
Cut open the roll (remove some dough if necessary from the middle), cover the underside first with the lettuce, then with the shrimps, pour the yoghurt mixture on top and cover with the top half of the roll.
Tastes especially good when the roll is still warm.