Meanwhile, in a large, deep skillet, heat the olive oil. Add the shallot and cook over moderately high heat until softened, about 1 minute. Add the eggplant pieces in an even layer and cook undisturbed until browned on the bottom, about 1 minute. Cook, stirring a few times, until tender, about 2 minutes longer. Add the vegetable stock and simmer for 1 minute. Add the tomatoes and mint, season with salt and pepper and cook over low heat for 4 minutes.