Heat oil. Add asafoetida (hing), cumin seeds, fennel seeds (saunf), crushed fenugreek seeds (methi dana), and dry red chilies (stalks removed), and saute for 4-5 seconds.
Break boiled and peeled potatoes using your palms into bite-sized pieces and add them to the pan along with green chilies (slit into half). Mix everything well and fry for 2 minutes.
Now add turmeric powder, Kashmiri red chilli powder, dry ginger powder, garam masala powder, and salt. Saute for a minute.
Add water and bring the curry to a boil.
Now reduce the heat to low and cook the curry uncovered for 15-20 minutes. Add dry mango powder (amchoor) and cook for another minute.
Check for salt and add more if needed. Garnish with cilantro (coriander) and serve with poori or kachori.