In a large mixing bowl, whisk together the Greek yogurt, lemon juice, minced garlic, paprika, cumin, black pepper, salt, turmeric, cinnamon, and red pepper flakes until fully blended and creamy.

Ensure there are no clumps in the marinade for best flavor infusion.

Place the chicken thighs in a zip-lock bag and pour the marinade over, ensuring each piece is well-coated. Seal the bag tightly and refrigerate for at least 4 hours, preferably overnight.

Slice the onion and spread it evenly at the bottom of the slow cooker.

Remove the chicken from the bag and lay it on top of the sliced onions. Cover and cook on high for 3-4 hours or low for 4-6 hours until tender.

Remove the chicken, shred it with forks, and return it to the slow cooker to soak in the juices for an additional 10 minutes.

Combine yogurt, minced garlic, grated cucumber, cumin, lemon juice, salt, black pepper, and optional red pepper flakes in a bowl and mix until smooth.

Warm pitas and fill each with shredded chicken, yogurt sauce, and fresh veggies. Serve and enjoy!