In a small bowl, combine the garam masala, coriander, and turmeric; in a measuring cup, stir together water, sugar, and vinegar. Cut eggplant into 2-inch pieces.
Heat the butter in a large, heavy nonstick skillet over moderate heat. Add the spices and cook, stirring, until fragrant, about 1 minute. Add eggplant and salt and toss to coat with the spice mixture. Stir vinegar mixture and add to eggplant mixture. Simmer mixture, covered, without stirring, 10 minutes, or until eggplant is just tender. Uncover skillet and cook eggplant mixture at a rapid simmer, without stirring, until liquid is almost evaporated and eggplant is slightly charred (but not burned) on bottom, about 15 minutes.
Remove skillet from heat and let eggplant stand, covered, 5 minutes.
Transfer the eggplant to a serving bowl, sprinkle with cilantro, and serve with rice.