Heat a tablespoon of oil in a pan. Add cumin seeds and allow them to crackle. Then add ginger paste and chopped green chillies. To this add coriander powder, red chilli powder, and turmeric powder. Saute for 30 seconds and add mashed potatoes. Add salt to taste. Stir well and cook for a minute. Add dry mango powder (amchoor) and garam masala powder. Switch off the gas. Also add chopped coriander leaves. Mix well. Filling is ready.