Heat vegetable oil in a pan, crackle mustard seeds and cumin seeds.
Add ginger paste and chopped green chili; sauté for 30 seconds.
Add chopped tomatoes, turmeric powder, red chili powder, and salt; cook until tomatoes turn soft and mushy.
Add water and jaggery; bring curry to a boil for 5 minutes.
Stir in thick sev right before serving so it stays crisp.