Begin by thinly slicing the red onions and separating the layers with your hands. Place them in a large bowl.
Add the turmeric, chilli powder, chopped green chilli, ground cumin, ground coriander, chopped fresh coriander, lemon juice, and salt to the bowl. Mix everything well until the onions are evenly coated.
Allow the mixture to sit for 15 minutes so that the salt and lemon juice can draw moisture from the onions.
After 15 minutes, add the bicarbonate of soda to the mixture. Gradually incorporate the gram flour, a little at a time, until the onions are lightly coated and can hold together when squeezed.
Heat the oil in a deep pan to a temperature of 170 to 180 degrees Celsius.
Take a small handful of the onion mixture, gently squeeze it together, and carefully lower it into the hot oil.
Fry the bhajis in batches for 3 to 4 minutes, turning them occasionally until they are deep golden brown and crunchy.
Once cooked, remove them from the oil and drain on a wire rack or kitchen paper. Sprinkle with a pinch of flaky sea salt while they are still hot.
