Boil potatoes in pressure cooker for 2 whistles.
Peel and mash them.
In a pan, pour 1 tablespoon oil. When it is hot add cumin seeds and let them splutter.
Now add the dry spices followed by mashed potatoes. Saute till the mixture leaves sides and starts to bind together.
On a flat griddle smear some cooking oil. Open up the buns without separating them. Lightly brown them by placing on the greased griddle.
Assemble by covering one side of the bun with potato mixture.
Garnish with ringlets of onions and tomato slices.
Serve with chutneys of your choice.