Heat 1 tablespoon of the oil in a non-stick frying pan over a medium heat. Add the onion and garlic and fry gently for 4-5 minutes, or until softened, stirring regularly. Stir in the cumin and coriander and fry for 1-2 minutes, or until fragrant. Remove from the heat and set aside to cool for 5 minutes.
Place in a food processor, add half of the chickpeas and all of the hummus and flour. Season with salt and pepper. Blend to a rough paste.
Add the remaining chickpeas and the pine nuts. Pulse for a few seconds until the chickpeas and pine nuts have broken down but retain some texture. Season to taste.
Divide the chickpea mixture into 8 portions. Roll each into a ball, flatten between your palms into a burger shape approximately 1.5cm/½in thick.
Heat the remaining oil in a large, non-stick frying pan. Add the burgers in batches and fry for 3-4 minutes on each side, or until golden-brown and crisp on both sides and heated through.
Serve the burgers in pitta breads stuffed with salad leaves, with a dollop of yoghurt and chilli sauce alongside.