Take the potatoes, boil it, peel it and cut it into cubes.
Take a pan, heat oil in it and add the green chilies, curry leaves and mustard seeds. Let them splutter. Once done, add turmeric powder, salt, and potatoes in it. Put little water in it, the potatoes will soak the masala. Keep boiling it for close to 5 mns.
In case if you want it to taste little different, you can use the cumin seeds instead of mustard seeds.