Heat ½ tbsp of the oil in a pan and cook the onion for 5 minutes until softened, adding the garlic for the last minute. Tip into a food processor along with the chickpeas, lemon zest and juice, cumin, ground coriander, fresh coriander, breadcrumbs. Beat the egg yolk and add to the mixture.
Whizz until combined, then shape into 12 balls. Place on a plate and chill in the fridge for 15 minutes.
Preheat the oven to 180ºC/gas mark 4. Heat the remaining oil in a large frying pan and fry the balls for 2-3 minutes each side until golden. Put on a baking tray, then cook in the oven for 10-15 minutes until golden.
Divide the tzatziki, mint, salad, tomatoes and falafels between the tortillas and serve.