Mix the ingredients for the dough in a bowl. Knead them into a smooth ball. The dough should have enough flour to not be sticky, but more importantly it shouldn't have too much flour so that it's easy to seam folds. Let the dough ripen in a fridge for 1 hour minimum.
Prepare the filling by mixing the mashed potato and mayonnaise.
Roll the ball out as a thin layer on a circular area with a diameter of roughly 22 cm. Sprinkle half the mozzarella as a thick layer on a circular area with a diameter of half the diameter of the dough on on top of the dough. Apply the mashed potato and mayonnaise mix on top of the cheese in a similar layer. Sprinkle the rest of the mozzarella in a similar layer on top of the mashed potato.
Join the edges of the dough on top of the center of the last layer of mozzarella cheese so that the dough wraps around the filling. Pinch and seam the folds. Gently push the dough so that it forms a circular right cylinder with rounded sides. Turn the bread upside down and roll it gently out a little more.
Fry the bread with both its sides coated with cooking oil on a frying pan for grossly 5 minutes per side until both its sides are golden brown.