Next add the yoghurt and olive oil to the yeast and stir then gradually pour the mixture to the flour and mix together to form a dough.
Knead the dough for 15 minutes, until it is nice and soft and not sticking to the surface of the bowl.
Brush a little olive oil on the surface of the dough and place in a large bowl, cover with a cloth and leave in a warm place until dough becomes double the size or for 1 – 1½ hours.
Heat1 tablespoon of oil in a large frying pan and fry the chopped onions on medium heat for 3 – 5 minutes until slightly browned.
Set aside and leave to cool for 10 minutes.
In a separate bowl place the yoghurt, tahini, vinegar and chopped tomatoes and mix well, then pour over the fried onions.