Heat vegetable oil in a pan, add mustard seeds and cumin seeds until they crackle.
Add ginger paste and chopped green chili, sauté for 30 seconds.
Add chopped tomatoes, turmeric powder, red chili powder, coriander powder, and salt. Cook until tomatoes turn soft.
Add water and jaggery, bringing the gravy to a simmer for 5 minutes.
Stir in thick sev just before serving so it retains its crisp texture.