Start by making the filling. Heat oil in a kadai and add cumin seeds and let it crackle.
Add onions and sauté for 5 mins. Add some salt, turmeric powder and chilli powder and mix well.
Add in tomatoes and mix well.Cook for 5 mins until it turn mushy.
Now add in the cooked potatoes and mix well.Remove it and allow it to cool completely.
Take wheat flour, salt in a bowl and mix well. Pour water gradually and make into a stiff dough. Let it rest for 5 mins.
Divide the dough into equal portions. Take two balls from it and roll into round pooris.
Add a spoonful of filling in the middle of one of the rolled poori and apply some water around the edges and seal it with another poori. Now take a lid of a steel jar and cut the poori so that you get a perfect round poori and this will puff up beautifully.
Now heat oil for deep frying and fry this poori on both sides till golden brown. Remove into a paper towel.