Heat the oil in a large saucepan. Add the tomato, garlic and ginger and cook over moderate heat, stirring, for 3 minutes. Add the curry and cook, stirring, until fragrant, about 2 minutes. Stir in the eggplant. Add the stock and bring to a boil. Add a pinch each of salt and pepper, cover and simmer over low heat, stirring occasionally, until the eggplant is tender, about 8 minutes.