Rinse the rice and kidney beans in water and soak them in enough water separately for 6-8 hours or overnight.
Next day drain the water and grind the rice and kidney beans together with cumin seeds, ginger, salt and green chilies (if using).
Add water as required to make the dosa batter.
Heat a non-stick skillet and pour a ladle full of batter in the center of the tava.
Using back side of the ladle spread the batter from center towards the edges in circular motion.
Drizzle oil on the dosa and cover cook for 1-2 minutes. Flip the dosa and cook the other side too.
Remove the dosa on a plate.
Make all the dosa in a similar way.
Serve the rajma dosa hot with some chutney or dip of your choice.
The leftover batter can be refrigerated for 1-2 days.