Wash brinjals and rub them with a little oil. Make long slits on them and roast them on low heat till the outer skin chars. Remove from heat and soak them in cold water. Peel and mash the brinjals.
Whisk yogurt till smooth. Dry roast cumin seeds to a coarse powder. Remove stems, wash and finely chop green chillies. In a bowl mix the mashed brinjals, yogurt, red chilli powder, roasted cumin powder, green chillies, asafoetida and salt. Mix well.