Heat the oil in a large nonstick frying pan or wok over medium heat.
Once shimmering, add the asafetida, followed immediately by the mustard seeds.
As soon as the mustard seeds begin to pop (this will only take a few seconds!) , add the cumin seeds, ginger, and green chilies.
Sauté for 30 seconds until fragrant.
Stir in the ground coriander, turmeric, and red chili powder.
Cook for just 10-15 seconds to toast the spices, then immediately add the boiled potato pieces.
Gently toss to coat the potatoes in the masala and fry for 1-2 minutes, allowing some edges to get slightly crisp.
Pour in the water and stir to combine, gently scraping any flavorful bits from the bottom of the pan.
Lower the heat.
Season with amchoor (or lemon juice), salt, and garam masala.
Stir gently to mix and let it simmer for another minute for the flavors to meld.
Serve hot.