Heat oil in a vessel. Add the mustard seeds and let them pop. Add the crushed garlic and curry leaves and toss them for 8-10 seconds.
Add the onions and fry till translucent. Add the chilli pwd, turmeric pwd, coriander pwd and salt. Combine well.
Add the chopped tomatoes and cook on medium heat uncovered for 4-5 mts. Reduce heat and cook covered for another 5 mts.
Add a glass of water, jaggery, adjust salt and cook covered till you get the desired gravy consistency.
Garnish with fresh coriander leaves and serve with hot chapatis, rice, pongal, khichidi or dosas