Mix onions, spinach, chickpea flour, ginger, coriander, and green chilli with enough water to form a thick batter.
Thoroughly mix in the salt, chilli powder, and turmeric.
Heat sunflower oil in a wok until it reaches 2.5 cm up the sides.
Test the oil temperature by dropping a small amount of batter into the wok.
Fry golf-ball sized portions of the mixture on low heat until golden.
Remove the bhajis from the oil and drain them on kitchen paper.
Increase the heat and fry the bhajis a second time until they are crisp and golden brown.
Sprinkle with chaat masala if desired and serve.