Wash and soak pinto beans in plenty of water overnight or at least 8 hours.
When they become soft, grind the beans into a fine paste along with ginger + green chilies + cilantro. Add more water if needed.
It's ok if it doesn't grind so smoothly, it still tastes great.
You can also grind ginger + green chilies + cilantro separately instead of adding it to the beans and then mix with the batter-
Transfer this pinto bean batter to a big bowl and add rice flour + cumin seeds + salt and mix well. Make a thin batter.
Heat a non-stick pan and pour a ladleful of the batter in the center and spread quickly into a circle. Pour little oil around the dosa and leave it for some time until it comes off easily from the pan.
Flip over and pour little more oil (optional) around the dosa and let it cook for some time. Remove from the pan and place on a serving plate. Repeat the same process with rest of the batter.