Rinse the soaked yellow lentils thoroughly and drain the water.
Combine the soaked lentils, green chilies, cumin seeds, coriander powder, turmeric powder, red chili powder, and salt in a blender or food processor. Blend until you get a smooth, batter-like consistency. If needed, add a few tablespoons of water to aid the blending process.
Transfer the lentil batter to a mixing bowl and add the finely chopped onions and spinach. Could you mix everything well to combine the vegetables with the lentil batter.
Heat oil in a deep frying pan for traditional frying, or preheat your air fryer if using.
For traditional frying: Drop spoonfuls of the lentil and spinach mixture into the hot oil, frying a few bhajias at a time. Fry them until they turn golden brown and crispy. Remove them with a slotted spoon and place them on a paper towel-lined plate to absorb excess oil.