Peel and finely chop the onions on a cutting board, then transfer them to a large mixing bowl. The onions should be fine, slightly sticky, and fragrant.
Toast cumin seeds in a dry pan over medium heat until aromatic, about 1 minute, then crush them lightly with a mortar and pestle or the back of a spoon. Add the toasted cumin and coriander powder to the onions.
Add chopped green chili, chopped cilantro, salt, and baking soda to the bowl. Stir everything thoroughly to combine, ensuring the onions are evenly coated with the spices and herbs.
Gradually sprinkle in chickpea flour, mixing with a spoon or your hands to form a thick, sticky batter. Add water a tablespoon at a time until the batter holds together but remains thick and slightly sticky.
Heat oil in a deep frying pan over medium-high heat until it shimmers and begins to bubble, indicating it’s hot enough for frying.
Using a spoon or your hands, scoop small portions of batter and carefully drop them into the hot oil. Be gentle to prevent splattering, and fry in batches to avoid overcrowding.
Fry the bhajis, turning occasionally, until they are golden brown and crispy around the edges, about 3–4 minutes per batch. Listen for a crackling sound that signals they are frying properly.
Use a slotted spoon to remove the bhajis from the oil and drain on paper towels to remove excess oil. Repeat with remaining batter.
Serve the onion bhajis hot, with your favorite chutney or yogurt for dipping. Enjoy their crispy exterior and tender, flavorful interior.
