Soak the rice and all the dhals in water for atleast four hours. Wash and drain the water. Add red chillies, asafetida and salt. Grind to a coarse paste. Chop the onion finely. Add to the batter. Add coconut and curry leaves to the batter. Add little water if required to make the batter little thicker than dosa batter.
Heat Dosa Tawa. Grease it. Pour a big ladle of batter in the middle of the tawa and spread evenly. Pour oil around the corners. Cook on medium flame. Turn over and cook other side also till it turns it colour to a nice brown.
You can eat as it is. Or serve with aviyal or chutney.
Tips: You can make this adai without onion and coconut also. If you like masala taste, you can add a teaspoon of aniseeds (sombu) while grinding the rice. You can increase or decrease the quantity of chillies according to your taste.