Heat oil in a pan, add the mustard & cumin seeds and after they pop, saute onions, garlic till translucent.
Add tomatoes and green chilies; cover and cook till tender.
Add boiled kohlrabi, red chili powder, tamarind paste, jaggery, salt and ½ cup of water. Cover and simmer for about 10 minutes or till the gravy thickens.
Serve with steamed rice or dosa or even roti.