Mix together the yoghurt, cucumber, tomato, coriander and olive oil. Refrigerate for 1 hour.
In a food processor add in chickpeas, onion, garlic, parsley, cumin, coriander and sea salt then process until smooth. Add in flour then process. Refrigerate for 1 hour.
Over medium heat, heat olive oil in a deep frying pan. Roll the falafel mixture into small balls, about 2 teaspoons full per ball. Fry falafel in batches until browned. Drain on newspaper then serve with sauce.
To make vegan, use either soy yoghurt or just take out the yoghurt altogether.