Soak the rice and the poha, if using, for at an hour. Drain out all the soaking water.
Place in a blender with the other ingredients and process to a smooth but very slightly grainy paste. Add very little water at a time. The batter should be fairly thin and runny if you want thin dosas. For thicker dosas, make it the consistency of regular pancake batter.
Let the batter stand overnight or for 8 hours.
Heat a griddle. When hot, pour about 1/2 cup of the batter in the center. If your batter is quite thin, it will spread into a round on its own. If thick, help along with the ladle to create a round.
Let the dosa cook until bubbles appear all over. Spray or pour a few drops of oil around the edges of the dosa to crisp up the edges and help it release from the pan.
When the bottom is golden brown, flip over and cook for about 30 seconds more.