Heat 1 tablespoon of the oil in a large frying pan. Add the onion and cook over a low heat for 5 minutes until softened. Tip into a large mixing bowl with the chickpeas and ground spices and mash using a fork or potato masher until the chickpeas are broken down. Stir in the chopped coriander and season to taste. Add the egg yolk, then squish the mixture together with your hands.
Mould the mixture into 8 small balls, then flatten into patty shapes. Heat the remaining oil in a frying pan and fry the falafels for 3 minutes on each side until golden brown and firm to the touch.
Mix the yogurt with the mint sauce and spoon over the falafels (hot or cold). Serve with the mini pittas, salad leaves and tomatoes.