Heat the oil in a large skillet. Add the garlic, ginger, green chile and cumin seeds and cook over low heat until fragrant, about 3 minutes. Add the scallions and onion and cook until softened, about 5 minutes. Add the tomato, season with salt and cook over moderate heat until the liquid evaporates, about 2 minutes. Add the vegetables, coriander, pepper and turmeric and season with salt. Cook, stirring, until the vegetables are heated through, about 3 minutes. Serve hot.