Fill a large saucepan two-thirds full with vegetable oil. Heat gently until the oil is hot. To test if the oil is ready add a cube of bread and it should sizzle and brown within 1 minute.
Whilst the oil is heating, on a chopping cut the onions in half through the root end then place each half, flat-side down on the board. Cut into medium-thick slices.
Place in a bowl and sprinkle over remaining ingredients. Season well with salt and use your hands to toss the ingredients together to combine. The onions should be well coated in the flour and spices. Drizzle over a few drops of water and mix again.
When the oil is ready wet your hands and take out small handfuls of the onion mixture from the bowl. Place straight into the hot oil and fry in batches, turning over for 1 min or until crisp and golden.
Drain on absorbent kitchen paper and keep warm on a baking tray in a low oven whilst cooking remaining bhajis. Serve with chutneys and salad.