1. Heat oil in a pan, season with mustard and cumin seeds, curry leaves and fry for few minutes.
2. Add green chilies, onions and fry for another 5 minutes.
3. Now add tomatoes and cook until they become soft. Then add potato pieces and stir well.
4. Add 1/2cup water and salt to taste and cook until the water evaporates.
5. Finally, add coriander powder and remove from heat.
6. Sprinkle coriander leaves and serve with any tiffin or rice.