Soak 1 cup of moong dal for 2-3 hours, then grind it into a smooth paste.
Add 1 teaspoon of salt, 1/2 teaspoon of cumin seeds, and a pinch of asafoetida to the paste and mix well.
Heat oil in a kadai and drop spoonfuls of the paste into the oil to make vadas. Fry until golden brown.
Soak the fried vadas in warm water for about 30 minutes, then squeeze out the excess water and keep aside.
For the kanji, mix 2 litres of water, 2 tablespoons of mustard powder, 3 tablespoons of red chilli powder, 2 tablespoons of salt, and 2 tablespoons of turmeric powder in a large jar.
Add the vadas to the jar, cover it and let it ferment for 2-3 days.
Serve the kanji vada chilled.