Heat 2tsp oil in a pan, add nigella and cumin seeds, once the seeds start to splutter, add the green chilies and cook for a few minutes.
In a mixing bowl, combine mashed potatoes, green peas, cilantro, corn starch, salt and the tempering. Mix well and divide the mixture into 8 equal portions. Roll each portion into a round tikki and flatten it slightly.
Heat a little oil on a nonstick tawa and cook the tikkis until lightly browned on both sides, about 2~3 minutes per side.