Heat oil in a pan and add mustard seeds. Wait till the seeds start to crackle. Add a pinch of asafoetida (heeng).
1/2 Teaspoon Mustard Seeds, 1/4 Teaspoon Heeng (Asafoetida), 1 Tablespoon Cooking Oil
Add finely chopped green chillies and ginger-garlic paste. Optionally curry leaves can be added. Saute for a minute or two.
2 Green Chillies, 1/2 Inch Ginger, 3-4 Garlic Cloves
Then add red chilli powder, turmeric powder and salt to the pan. A very small quantity of black pepper can also be added to this mix. Add the boiled and mashed potatoes to the pan and mix thoroughly. You can also add some boiled green peas.
1/2 Teaspoon Red Chilli Powder, 1/2 Teaspoon Black Pepper Powder, 1/2 Teaspoon Turmeric Powder, 1 Teaspoon Salt or as per taste, 3 Medium Sized Potatoes, boiled