Boil, peel and mash the potatoes well.
In a mixing bowl, combine the mashed potatoes, amchur, red chilli powder, fennel, coriander powder, cumin powder , garam masala and salt and mix until well combined. Keep it aside.
Wash the chillies and wipe them with a cloth. Slit the chillies lengthwise and remove seeds.
Stuff them with prepared potato filling and keep them aside.
Heat oil in a pan for deep frying.
Combine the besan, salt, turmeric powder and baking soda in a mixing bowl. Make a smooth and little thick batter by adding water little by little.
Dip the each stuffed chilli into the besan batter and carefully drop it into the hot oil.
Deep fry in hot oil until crisp and golden color.
If you want to expose the chilli, dip the chilli into the batter and slide it onto the edge of the batter bowl to expose the one side of the chilli.
Remove the fried vadas from oil and place them on a paper towel.
Serve hot with ketchup or green chutney.