In a bowl, mix olive oil, garlic, cumin, paprika, turmeric, coriander, cinnamon, salt, and pepper to create a marinade.
Add chicken thighs to the marinade, ensuring they are well coated. Cover and refrigerate for at least 1 hour, preferably overnight.
Preheat the grill or a skillet over medium-high heat.
Cook the marinated chicken for about 6-7 minutes on each side or until fully cooked and juices run clear.
Remove the chicken from the heat and let it rest for a few minutes before slicing it thinly.
Warm the pita breads on the grill or in a skillet.
Assemble the shawarma by placing sliced chicken, lettuce, tomato, and cucumber in the pita.
Drizzle with garlic sauce before serving.