1. Grind ginger, garlic and green chilies together into a paste.
2. Peel and smash potatoes. Do not smash completely. Let some small chunks remain.
3. Add ginger, garlic and green chili paste, coriander leaves, and salt to the potatoes.
4. Then take 2 teaspoons oil in a kadai. Add mustard seeds. When they splutter, add turmeric powder and curry leaves.Pour this tempering on the mashed potatoes and mix gently.
5. Make small balls of mashed potato mixture and flatten the balls.
6. Add some salt, turmeric powder and chili powder to the gram flour. Add water gradually and keep mixing with a sppon or wire whisk. Remove lumps if any. The batter should not be too watery or too thick. If lifted by a spatula, it should flow in a ribbon like consistency.
7. Heat some oil in a pan. Make sure that the oil is not too hot. Otherwise, the vadas become dark from the outside before they are actually done from the inside.
8. Now dip each ball in the batter, letting the excess batter drip off and slowly add to the hot oil. Do not overcrowd the pan, else the temperature of the oil reduces which in turn slows down the frying process. Like this, deep fry all the vadas until golden. Remove on a paper towel and drain. Batata Vadas are ready.
9. For Vada Pav, split Pav keeping the base intact & spread garlic chutney or green chutney on the inner surfaces of it. Place the vada in it. Serve hot with some chopped onions and lemon piece.