Place the sugar, yeast and water in a large bowl and mix well. Keep aside in a warm place for 10 minutes. 

Add the remaining ingredients ( flour, plain yogurt and salt) to the bowl. Mix well to form dough.

Transfer the dough on a lightly floured surface and knead for 5 minutes or until smooth.

Put the dough back to the bowl, brush with olive oil, cover with a clean towel and allow to rise for 30 minutes or until doubled in size in a warm place.

Divide the dough into 10 equal pieces, form balls and roll out each ball on a lightly floured surface into a 23 cm/9 inch circle ( 2 mm thick).

On one side of each circle grate a boiled potato, about 2 tablespoons, put 1 tablespoon of cooked mushrooms, leaving a 2 cm border. Sprinkle with dry mint or parsley and Turkish roasted pepper flakes.

Fold the other half of the dough over and seal the edges.

Lightly grease the pan with olive oil and heat it over high heat. Brush each gozleme with olive oil and cook for 2 minutes per side or until golden.Repeat with the remaining gozleme.

Cut each in half and serve immediately with lemon wedges.