Heat oil in a Kadhai. Add Jeera once it splutter add tomatoes, turmeric & green chillies. Saute & cook until tomatoes get tender. Add red chilli powder, Rock salt saute well. Add potatoes, & Makhana. Saute for 1 minute. Add 1 cup water. Let it boil for 3-4 minutes on medium flame. Once gravy is done. Switch ogg gas.