In a large bowl, whisk together the plain Greek yogurt, fresh lemon juice, minced garlic, paprika, ground cumin, black pepper, salt, ground turmeric, ground cinnamon, and red pepper flakes until smooth and well combined.

Take the chicken thighs and place them into a ziplock bag or a shallow dish. Pour the prepared marinade over the chicken, ensuring each piece is thoroughly coated. Seal the bag or cover the dish and refrigerate for at least 4 hours, or preferably overnight.

Slice the onion and layer the rings evenly at the bottom of the slow cooker.

Remove the marinated chicken from the refrigerator and place the thighs on top of the onions in the slow cooker. Cover and cook on high for 3-4 hours or on low for 4-6 hours.

Once done, carefully remove the chicken thighs and shred them into bite-sized pieces. Return the shredded chicken back into the warm slow cooker.

In a separate bowl, combine the plain Greek yogurt, minced garlic, grated cucumber, cumin, lemon juice, salt, black pepper, and red pepper flakes. Mix well until smooth.

To serve, warm your pita, layer the shredded chicken, add toppings, and drizzle the yogurt sauce.