In a vessel, combine besan, rice flour, salt, red chilli pwd, ajwain, baking soda and enough water to make a slightly thick smooth batter.
Heat oil for deep frying in a heavy bottomed vessel and once oil is piping hot, reduce to medium flame.
Dip each plantain slice in the batter till it's well coated and place in hot oil.
Fry till golden brown. Increase flame towards the end of the cooking process when the bajjis attain a golden shade, drain and place on absorbent paper.
Serve hot with coconut chutney or ketchup.