Heat oil in a wok or kadhai on medium heat. Add mustard seeds and when they begin spluttering, add methi seeds and garlic. Fry them for 10-15 seconds.
Add the tomatoes followed by the cumin, coriander and chili powders and salt and mix well.
Cover for 5 minutes and then open the lid and add jaggery and mix well.
Reduce the heat to low and cover the wok and let it cook for 5 minutes. Stir again.
Uncover the lid and continue to cook for another 5 minutes. At this point, the tomatoes have softened and the gravy is ready to be served with warm rotis.