Delicious Chicken Salad with Yogurt Marinade and Pita Bread 

Instructions:

1. Marinate the Chicken: In a large bowl, whisk together the yogurt, lemon juice, vinegar, garlic, cumin, oregano, paprika, cinnamon, salt, and pepper. Add the chicken thighs, making sure they are coated evenly. Cover and refrigerate for up to 4 hours, or overnight for deeper flavor.
2. Preheat the Oven: While the chicken marinates, preheat your oven to 220°C (fan 200°C/gas 7). Line a baking sheet with foil (optional) for easier cleanup.
3. Roast the Chicken: Remove the chicken from the marinade and arrange it on the prepared baking sheet. Discard the leftover marinade. Roast for 20-25 minutes, or until the chicken is cooked through and nicely browned.
4. Prepare the Salad: Meanwhile, combine the sliced onions with 1 tablespoon vinegar and a pinch of salt in a bowl. Let them sit for a few minutes to soften slightly.
5. Then, stir in the tomatoes, sumac (or lemon juice), and adjust seasonings to taste.
6. Make the Tzatziki Sauce (optional): In a separate bowl, combine the grated cucumber (squeezed to remove excess water), remaining vinegar, garlic, yogurt, dill, and salt and pepper to taste.
7. Assemble and Serve: Divide the shredded lettuce among plates. Top with the roasted chicken slices, the tomato-onion mixture, and a dollop of tzatziki sauce (if using). Serve with warmed pita bread.

Tips:

1. Leftovers can be stored in an airtight container in the refrigerator for up to 3 days.
2. Feel free to adjust the spices in the marinade to your preference.
3. For a vegetarian option, substitute tofu or tempeh for the chicken and marinate it in the same way.