Chop half the mint and put in a bowl with the yogurt, half the lemon juice, all the lemon zest, spices and ginger. Mix well and season with lots of black pepper and a pinch of salt. Add the chicken pieces, mix well and put in the fridge for 20-30 mins. Meanwhile, soak 4 large wooden skewers in water for at least 20 mins (or use metal ones).
When you’re ready to cook the chicken, heat your grill to a medium heat and line the grill tray with foil. Thread the chicken onto the soaked wooden or metal skewers and grill for 15-20 mins, turning halfway through, until browned and cooked through.
Warm the flatbreads under the grill for a couple of seconds, then serve them topped with the lettuce, chicken, red onion, remaining lemon juice and mint, and any optional extras such as extra yogurt or pickled cabbage, chilli sauce and hummus.