Wash and soak ragi, moong,urad dal, and methi seeds in enough water for 8–10 hours.
Drain the soaked ingredients and transfer to a mixer jar. Add a little water and grind to a smooth, fine paste.
Transfer the batter to a large bowl, add salt, and mix well.
Cover and ferment the batter for 10–12 hours or overnight, until light and airy.
After fermentation, adjust the consistency by adding water if the batter is too thick.
To make the chutney, In a mixer jar, combine coconut, roasted chana dal, green chillies, garlic,tamarind, coriander leaves, salt, and a little water.
Blend to a smooth paste and transfer to a serving bowl.
For tempering, heat oil in a small pan. Add mustard seeds, urad dal, and curry leaves. When they splutter, pour the tempering over the chutney. Mix well.
To make the dosa, Heat a dosa tawa (griddle) on medium heat.
Pour a ladleful of batter in the centre and spread in a circular motion to form a thin dosa.
Drizzle a little ghee or oil around the edges.
Cook until golden and crisp. Remove from the pan and serve hot with coconut chana dal chutney.