Wash and cook potato firstly. You can cook by your way - Either by open pot boiling until fork tender or pressure cook for 3 whistle with lots of water and salt.
Once done, peel off the skin and mash it.
Cook the vermicelli in 2 cups of water until tender. Do not over cook. Drain the water completely and set aside.
Add it to cold water immediately and drain it again, keep aside.
Slice onion lengthwise.
In a mixing bowl, mix all the ingredients gently without adding water.
Heat oil in kadai and add as small pakoras.
Cook both sides in medium flame and drain in paper towel.