Preheat the oven to gas 4, 180°C, fan 160°C. Peel and finely slice 1½ onions and place in a large bowl. Finely chop the remaining half and mix it with the red wine vinegar and a pinch of sea salt. Set aside.
Scrub the carrots, then coarsely grate into the large bowl. Peel the garlic and ginger, then finely grate over the carrots. Finely chop the green chilli (deseed if you like) and most of the coriander (stalks and all), saving a few pretty leaves for later, then add to the bowl.
Tip in the flour, turmeric and cumin, then season with salt and black pepper. Add 80ml of water, then give it all a good mix.
Drizzle 1 tbsp of oil into a large non-stick frying pan on a medium heat. Divide the bhaji mixture in half in the bowl. Take 4 large spoonfuls from one half and flatten slightly in your hands, then fry for 2-3 mins on each side or until golden and crisp. Repeat with the remaining mixture.
Transfer the bhajis to a baking tray and pop in the oven for 10 mins, or until cooked through. Add the chapatis for the final min to warm through.
Serve the bhajis on the warm chapatis. Swirl the mango chutney through the yogurt and spoon over the drained red onion pickle. Finish with coriander leaves and serve with lime wedges for squeezing over, if you like.