To make the green chutney:
Grind all the ingredients together sans water. Remove it in a bowl.
To make the vadas :
Mash the potatoes, add the onions, garam masala, chilli powder ,salt, amchur powder and coriander leaves and mix well. Mix the ingredients of the batter with a little water. It should be of semi thick consistency. Make small balls of the filling, keep aside. Heat oil in a kadai.Take a ball, dip it in the batter and slowly let a few of them in the oil. Fry till a dark hue engulfs them. Remove on an absorbent paper.
To make the vada pav :
Cut the pav bun into halves . Heat a skillet, smear some butter on it and roast it slightly. Apply tomato ketchup on one half and the green chutney on the other half. Take ,a fried dumpling, press it between palms and keep it between the two halves. Heat it on the skillet for a few seconds. Serve hot.