Rinse the chana dal under running water, then soak it in enough water to fully submerge it until the grains soften slightly but still feel firm when bitten.

Drain the chana dal completely in a colander and set aside a small handful of whole soaked dal to fold into the mixture later for texture.

Grind the drained dal in a mixer-grinder with minimal water, pulsing briefly so the mixture stays coarse and grainy rather than turning into a smooth paste.

Fold the chopped onion, green chilies, curry leaves, ginger, fennel seeds, asafoetida, salt, and coriander leaves into the ground dal along with the reserved whole soaked dal until evenly combined.

Cover the mixture and let it rest so the salt draws out moisture from the onions and the flavors settle into the dal.

Heat the oil in a kadai over medium heat until a small piece of the mixture dropped in sizzles gently and rises without browning too fast.

Take a small portion of the mixture, roll it into a ball between your palms, then flatten it gently into a thick disc about the size of your palm.

Slide the shaped vadas gently into the hot oil a few at a time and fry, turning occasionally, until deep golden brown and crisp on both sides.

Lift the fried vadas out with a slotted spoon and place them on a plate lined with paper towels to drain excess oil.

Shape and fry the remaining mixture in small batches, letting the oil return to temperature between batches so every vada fries evenly.

Arrange the fried vadas on a serving plate and serve immediately with coconut chutney or a hot cup of chai.