Prepare your chicken thighs by removing the excess fat bits and cartilage.
In a large glass bowl, mix the Greek yogurt with the pressed garlic cloves, salt, black pepper, cumin, chili powder (if using), cinnamon, smoked paprika, and the juice of one lemon. Add the chicken and mix until it is covered well on all sides.
Cover the bowl with plastic wrap and refrigerate for at least two hours. If you have extra time, you can marinate the chicken for up to 24 hours in the fridge.
Line a baking sheet with parchment paper and oil it lightly. Preheat your oven to (400℉)200℃.
After the chicken is marinated, remove from the fridge and lay each piece upside down on the baking sheet.
Spray a little bit of extra oil on the top of the thighs and bake for 10 minutes.
Turn your oven to broil and broil the chicken thighs for 5-10 extra minutes until they look done and toasty. Make sure the internal temperature of the chicken thighs has reached 165℉ (74℃).
Remove them from the oven and let them rest a little bit. Slice them on a bias and serve them along your favourite shawarma toppings.