Heat the oil in a pan and add mustard seeds, let them crackle. Add the asafetida, curry leaves, chopped green chilies, garlic and saute for a few seconds.
Add potatoes, turmeric powder and salt mix well cook for 2 to 3 minutes on medium flame. Once done switch off the flame and let it cool. Shape the potato mixture into medium size balls.
Combine besan, salt and little oil in a bowl add required water to make a batter.
Heat oil in a pan or wok dip each potato round in batter. Deep fry the balls until golden brown.
Slice each pav into half taking care one end is still connected to the bun. Heat tawa cook the pav from both sides till the pieces are lightly browned.
Spread some garlic chutney on both the halves. Place the potato vada in between pav serve immediately with green chilies, garlic chutney and green chutney.