In a large mixing bowl, combine the lemon juice, olive oil, Greek yogurt, ground cumin, ground coriander, smoked paprika, turmeric powder, garlic powder, onion powder, ground cinnamon, cayenne pepper (if using), salt, and black pepper. Whisk well to form a thick marinade.

Add the trimmed chicken thighs to the bowl, ensuring each piece is thoroughly coated with the marinade. Cover the bowl and refrigerate for at least 30 minutes, or ideally 2-4 hours, or even overnight for best flavor.

Transfer the marinated chicken and all the marinade to the slow cooker insert. There is no need to add any additional liquid as the chicken will release its own juices.

Cover the slow cooker and cook on LOW for 4 to 5 hours, or on HIGH for 2 to 3 hours, until the chicken is very tender and easily shredded with a fork.

Carefully remove the cooked chicken from the slow cooker, reserving the juices. Place the chicken on a cutting board and shred it using two forks.

For crispy edges (highly recommended for authentic shawarma texture), heat a large non-stick skillet over medium-high heat. Add 1-2 tablespoons of the reserved slow cooker juices to the pan. Add the shredded chicken in a single layer (you may need to do this in batches) and cook for 3-5 minutes, stirring occasionally, until some pieces are slightly browned and crispy. Alternatively, spread the shredded chicken on a baking sheet and broil for 3-5 minutes, watching carefully to prevent burning.

Warm your pita breads according to package directions.

To assemble, spread a generous spoonful of hummus or tahini sauce on a warm pita. Pile a good amount of the shredded chicken on top.

Add your desired toppings such as diced tomato, cucumber, red onion, fresh parsley, and pickled turnips or pickles. Drizzle with extra tahini sauce if desired. Fold or roll up the pita to enjoy.