To make the chutney place the red chillies in a mixer. Add garlic, ginger, roasted chana dal and salt. Add a little water and lemon juice and grind till smooth. Transfer into a bowl.
Heat a dosa tawa. Drizzle some oil and sprinkle a little water and wipe it with a piece of cloth. Pour a ladleful of batter onto the tawa and spread to cover the entire surface. Ensure the dosa is not too thin.
Drizzle some oil all around and let it cook till the underside is done. Spread some chutney all over. Place some batata bhaji in the centre and fold the dosa into a half moon shape.