In a medium bowl, whisk together the olive oil, lemon juice, minced garlic, paprika, cumin, pepper, salt, tumeric, and cinnamon.
Add the chicken and onion to the slow cooker.
Pour the marinade over the chicken and onion.
Put the lid on the slow cooker and cook on LOW for 4-6 hours, or on HIGH for 6-8 hours. The chicken is done when it reaches an internal temperature of 170 F and is easily shredded with a fork.
Let the chicken rest for about 5 minutes and then use a fork to shred the chicken in the slow cooker, stirring it into the juices.
Garlic Sauce
Place the garlic and salt into a food processor and puree until smooth.
Slowly drizzle in 1/2 cup of the oil while the processor is going.
Add in 1 tsp of the lemon juice and puree.
Drizzle in the remainder of the oil, puree, and then add the remainder of the lemon juice.
Puree until its fluffy and white!
Assembly
Warm the pita/flatbread in the microwave for about 30 seconds, and fill with lettuce, tomatoes, cucumbers, the chicken and drizzle with garlic sauce.