Roast the eggplants either on stove top (if you have a gas stove) or in the oven at 400F.
While the eggplants are roasting, heat 1tbsp of oil in a pan, add the tempering ingredients. After the mustard seeds and jeera splutter, add onions and green chilies fry till golden brown. Remove from heat.
After the eggplant are roasted, leave them aside till they are cool enough to handle.
Remove the skins and roughly smash the flesh with a fork.
Add tamarind paste, jaggery, salt and the onion mixture. Mix well and serve.