Add all-purpose flour, sugar, mashed banana, and salt to a bowl.
Add about quarter cup of water little by little until it forms paste. The batter should not be either thicker or too thin. It has to be in the thick flowing consistency.
Drizzle few drops of oil, and pour a ladle full of batter over the hot pan. Again drizzle a teaspoon of cooking oil around the dosa. In medium heat cook it for about 2 minutes. Flip it and cook again for another 1-2 minutes until they get cooked completely. Once done, remove it from tawa and transfer it to plate and serve banana dosa immediately.