Heat oil in a wide pan or kadai, add mustard, cumin, nigella seeds and once they crackle, add hing and saute for a few seconds. Add onions and fry for 1-2 minutes till they turn translucent. Add spice powders - turmeric, kashmiri chilli, coriander, salt and give a quick mix. Add ¼ cup of water and saute for a few seconds till the rawness of the spice goes.
1 tablespoon groundnut or any neutral flavoured cooking oil, ½ teaspoon mustard seeds, ½ teaspoon cumin seeds, ⅛ teaspoon nigella seeds, ⅛ teaspoon asafoetida, ¾ cup sliced onions, ¼ teaspoon turmeric powder, ½ teaspoon kashmiri chilli powder, 1 teaspoon coriander powder, ½ teaspoon salt, ½ cup water