In a glass baking dish, mix together malt vinegar, ¼ cup plain yogurt , vegetable oil, mixed spice, cardamom, salt and pepper. Place the chicken thighs into the mixture and turn to coat. Cover and marinate in the refrigerator for at least 4 hours or overnight.

Preheat oven to 350 degrees F (175 degrees C). In a small bowl, mix together the tahini, ¼ cup plain yogurt , garlic, lemon juice, olive oil, and parsley. Season with salt and pepper, taste, and adjust flavors if desired. Cover and refrigerate.

Cover chicken and bake in the marinade for 30 minutes, turning once. Uncover, and cook for an additional 5 to 10 minutes, or until chicken is browned and cooked through. Remove from the dish, and cut into slices.

Place sliced chicken, tomato, onion, and lettuce inside of pita breads. Roll up, and top with the tahini sauce .