In a medium bowl, combine Idly Rice, Thuvar Dhal, Channa Dhal, Urad Dhal, and Moong Dhal. Rinse the Rice and Dhal thoroughly until the water is clear, then soak them with the Red Chillies for at least 4 hours.
Grind the soaked Rice and Dhal into a smooth paste with Fennel seeds and a small piece of Ginger.
Transfer the batter to a bowl and add the chopped Onion, grated Coconut, Curry Leaves, Drumstick leaves, Asafetida, and Salt to taste. Mix well.
Heat a Dosa Tawa over medium heat and grease it with Oil. Pour a large ladle of batter onto the tawa and spread it evenly. Drizzle Gingelly Oil around the edges of the Adai. Flip it and cook the other side as well.
Serve hot with Aviyal, Butter, and Jaggery, or any other South Indian Chutneys.