Place the chicken in a large bowl.
In a small bowl, mix all the spices and add them to the chicken. Add in the garlic, lemon juice, olive oil. Combine and make sure all the chicken pieces are coated with the spices.
Let the chicken marinate for at least one hour up to overnight in the fridge.
When you're ready to cook, preheat the oven to 425°F and line a baking sheet with a piece of aluminum foil and coat with cooking spray. Place the chicken on the baking sheet and bake in the oven for 25 to 30 minutes until fully cooked and the internal temperature registers at 165°F.
Take the chicken out of the oven and cover with a piece of aluminum foil and let it sit for 5 minutes before slicing.
In another bowl, mix Greek yogurt, tahini, garlic, lemon juice, salt and water. If your sauce is too thick, add a bit more water. Taste and add more salt or lemon juice of needed.
Fill the salad bowls with lettuce and top with tomatoes, red onion, cucumbers, pita bread and sliced chicken shawarma. Drizzle with yogurt tahini sauce and serve.