Steam or boil potato until just done without making mushy.
Add atta to a mixing bowl along with salt and oil. Pour water just as needed and make a soft dough. Knead well until it becomes soft and pliable. Cover and set aside for 20 mins.
Divide the dough to 4 to 5 equal parts. Lightly sprinkle the rolling area and the dough ball with flour. Using a rolling pin roll the ball evenly to a round layer.
Heat a pan / griddle or tawa on a medium high heat. Gently transfer the roti to the tawa. When you see tiny bubbles, flip it and press down gently with a spatula.
Cook on both the sides flipping until both the sides are cooked with golden to brown spots. Add ghee or oil now.
Spread a kitchen cloth or tissue over a plate. Transfer the roti to it. Make all the rotis and stack them in the plate.
Heat a pan with oil. Allow mustard and cumin to crackle. Add hing, onions and salt. Saute until onions turn golden.
Fry ginger garlic paste until the raw smell goes off. Add all the veggies. Next add turmeric, chili powder, coriander powder and garam masala.
Saute for 1 to 2 mins. Cover and cook on a low flame until the veggies are cooked. Set this aside to cool.
How to make kathi roll
Smear chutney or sauce over the roti. Add a sufficient amount of cooked veggies to one side of the roti. Begin to roll it tightly and prick a tooth pick to hold in shape. Serve kathi rolls hot or cold.