Wash and soak idli rice, raw rice and channa dal in water for around 3-4 hours.
Similarly, wash and soak toor dal, urad dal and the fenugreek seeds separately for the same amount of time.
Drain most of the water from the soaked rice. Transfer the rice and some of the reserved water (around 2 to 3 tablespoons) to a mixer and add the green chillies and red chillies and one sprig of curry leaves and grind to a coarse mixture.
The texture of the ground batter must be like Rava or Semolina. Transfer the ground batter to a separate vessel.
Now drain the soaked toor and urad dal and grind this to a similar coarse batter with 2 to 3 tablespoons of the reserved water.
Mix the ground dal mixture along with the previously ground rice batter. Add little water to adjust the consistency if required. Make note not to add lot of water, as this batter is ought to be slightly thick. Now add some salt and asafoetida and rest this batter for couple of hours.
Before making the dosas, mix half a cup of freshly grated coconut and some chopped coriander and curry leaves. Adjust the batter consistency with little water if required. The batter should be of a thick pouring consistency and not drip immediately when dropped from a ladle. If you would like to replace the grated coconut with onion, saute one large sized onion finely chopped in little oil and mix with the batter.
Heat a cast iron tawa and spread a little oil and spray some water. Pour one ladle of the batter and spread it slightly thick (unlike dosa). Make a hole in the centre using a spatula for even cooking and add some oil. Adai generally requires little extra oil for cooking. Cook on medium flame till the edges start to brown.
Flip the dosa and cook the other side also on a medium flame. Add some more oil if required. Serve hot with chutney, avial or ghee and jaggery.