In a large bowl, mix the plain yoghurt, lemon juice, minced garlic, ground cumin, ground coriander, ground paprika, ground turmeric, ground cinnamon, cayenne pepper, salt, and black pepper.
Add the chicken thighs to the marinade, ensuring they are well coated. Cover and refrigerate for at least 1 hour, preferably overnight.
Preheat the oven to 200°C (180°C fan) or heat a grill pan over medium-high heat. Drizzle olive oil over the chicken thighs.
Cook the marinated chicken thighs in the oven for 25-30 minutes or grill them, turning occasionally until fully cooked and slightly charred. Let them rest for a few minutes before slicing.
In a small bowl, mix the tahini with water to create a smooth sauce.
Warm the pitta breads in the oven for a few minutes, then slice them open.
Fill each pitta with sliced chicken, shredded lettuce, sliced tomatoes, red onion, cucumber, and drizzle with the tahini sauce.