Place the whole eggplant directly over moderate heat on a gas stove or grill. Roast for about 10 minutes, turning every couple of minutes with metal tongs, until completely charred and the flesh is soft.
Once cool enough to handle, peel off the skin and discard it. Don’t worry if small bits of skin remain, as they add a hint of smokiness. Remove and discard the stem, then coarsely chop the flesh. Set aside.
Heat the oil in a large skillet over medium-high heat. Add the chopped onion and cook, stirring occasionally, for about 10 minutes until softened and lightly golden.
Add the green chiles and sauté for 2 minutes until their raw aroma disappears.
Mix in the tomatoes and 1/2 teaspoon of kosher salt, stirring occasionally for 8 minutes until the tomatoes soften and release their juices.
Add the roasted eggplant to the skillet. Stir in the chopped cilantro and cook for an additional 3 minutes, allowing the flavors to meld together.
Taste and adjust seasoning if needed. Serve hot with your favorite accompaniments like roti, naan, or steamed basmati rice.