Roast the Eggplant:

Pierce the eggplant with a fork several times. Roast it over an open flame or in a preheated oven at 400°F (200°C) until the skin is charred and the inside is tender, about 15-20 minutes on the stove or 35-40 minutes in the oven. Turn occasionally for even roasting.
Once cooked, let it cool, peel off the charred skin, and mash the pulp.

Prepare the Bharta:

Heat oil in a pan over medium heat. Add the chopped onions and sauté until they turn golden brown.
Add the ginger, garlic, and green chilies. Sauté for another 2-3 minutes.
Stir in the tomatoes, turmeric, coriander, cumin, and salt. Cook until the tomatoes are soft and the oil starts to separate from the masala.
Add the mashed eggplant to the pan. Mix well and cook for 8-10 minutes, stirring occasionally.
Sprinkle garam masala over the mixture and cook for another 2 minutes.

Garnish and Serve:

Garnish with fresh cilantro. Serve hot with roti, naan, or paratha.