Wash and slice the eggplants into thin slices. Keep the sliced eggplants immersed in water until ready to cook.
Roast the ingredients mentioned to a reddish brown color and then grind it into a smooth powder.
In a pan, heat the oil and add the mustard seeds. Once the seeds crackle, add the turmeric powder, asafetida and curry leaves. Fry for about 10 seconds and then add the sliced eggplants. Make sure that you drain the vegetable well before adding as excess water could make the curry mushy.
Let it fry in open pan (without covering the pan) for about 5 minutes. Now add salt and briefly cover the pan to cook the vegetable. Make sure that you could it only until done and not mushy. If the eggplants are tender, you might not even need to cover the pan.
Once the vegetable is ¾th cooked, add the ground spice powder and mix it gently. Cook further until it is roasted and then take off the flame.
Serve Eggplant Poriyal with hot rice and rasam!