Soak sabudana or tapioca pearls in 1 cup water for at least 2-4 hours.
In the meantime boil, peel and mash potatoes.
Also peel, boil or roast beetroot and grate it.
Transfer the soaked sabudana into a sieve or strainer. Wash gently under running water.
Transfer them to a kitchen cloth, spread the soaked sabudana and pat them dry.
Add mashed potatoes, grated beetroot, soaked sabudana in a mixing bowl.
Add chopped green chillis, ginger, cumin seeds, chopped coriander, salt, chopped cashew nuts, lemon juice and flour.
Mix the mixture well using your hand.
Rub your hands with some oil.
Take about one tablespoonful of the mixture and roll it into a ball. Flatten it slightly between your palms.
Repeat the above step with the remaining mixture.
Heat oil in a wok or karai over medium heat.
Add a small piece of the vada mixture in the oil. If it comes up immediately, the oil is ready.
Drop a few vada into the hot oil. Lower the heat. Fry turning them over frequently till they appear light golden in colour.
Remove the vada from the oil using a slotted spoon. Place them on the kitchen towel so it soaks up the excess oil.
Fry the rest of the vadas.
Serve them with a green chutney or a yogurt dip.