Whisk 1 tbsp olive oil with the lemon zest, oregano, half the garlic and season. Coat the chicken in the marinade and then thread onto wooden skewers. Grill or fry for 4 minutes on each side until slightly charred and cooked through. To make the tzatziki, mix the yoghurt, lemon juice, remaining garlic, cucumber, mint and season. Spoon the tzatziki onto the breads, add the salad and top with the chicken.