Heat the oil in a wide, shallow pan and add the cumin seeds and the onion. Sauté for about 5 minutes, until the onion is soft, then add the ginger-garlic paste and fry for a few seconds.
Add the green chillies and potatoes and sauté over a high heat for a couple of minutes. Tip in the cauliflower, turmeric and salt, mix well, then reduce the heat. Cover the pan and cook for about 10 minutes, stirring occasionally to prevent sticking.
Add the tomatoes and garam masala and cook for about 5 minutes, until the vegetables are tender. Sprinkle in the chopped coriander and the ginger, squeeze over the lime juice and serve – either with chapattis or as a side dish.