Heat oil in a pan and add mustard seeds. Once they start spluttering, add curry leaves and saute
Add onions and garlic and cook for a few minutes till the onions soften and become translucent
Add tomatoes, chilli powder, coriander powder, turmeric, green chillies and salt
Cook covered for 10 minutes till the tomatoes soften and become jammy
Add jaggery and 1/4 cup water and simmer for another few minutes
And it's ready!