Wash and dry the eggplant. Smear oil on the skin and a pierce it with a knife at a couple of spots.
On a medium flame, roast the whole and unpeeled eggplant. Turn it a few times till the skin is charred all over and the flesh is thoroughly soft.
Let it cool and then remove the blackened skin. Keep the skinless eggplant under water to take off any remaining bits of charred skin.
Mash the flesh with a fork to make a smooth pulp. Keep aside.
In a Kadai or wok, heat oil and butter. Add the onions, and saute till they become transculent. Add the tomatoes and fry till they wilt. Sprinkle in the salt and red chillie powder. Stir in peas and let them cook till tender. If using frosted peas, defrost before use. Blend in the mashed eggplant into the masala and stir well. Cook on medium heat for around 10 minutes.