Vertically slit the chili and remove the seeds,.but not the stems. Set aside.
Mix all the filling ingredients and set aside.
To make the vada batter, mix all the dry ingredients: Besan, cumin seeds, baking powder and salt. Add the water slowly to make a thick smooth batter, the consistency of pancake batter.
Add cilantro and mix it well.
Stuff the chilies with potato mix.
Heat one inch of oil in a frying pan over medium heat. To test, put one drop of batter in the oil. The batter should form a small ball on the surface of the pan, but not change color right away.
Dip the filled chilies in the batter one at a time, making sure each is covered with batter all around. Drop slowly into the frying pan.
Fry the mirchi vada until all sides are golden brown, four to five minutes, turning occasionally. Take them out and place them on a paper towel.