Heat oil in a pan, add mustard seeds and wait to crackle, add asfoitida, curry leaves, chilli chopped, and saute for a while. Then add chopped onion and saute till translucent, then add tomato and salt, cook till tomato became soft. Then add cooked potato and fresh toor dana. Add turmeric powder and salt to taste. Mix well and cook for 2min. Then keep aside.