Prepare the Oven: Place the first oven rack on the bottom shelf of the oven. Remove the second rack, as you’ll need it later to stabilize the chicken tower. Preheat your oven to 400°F (200°C).

Marinate the Chicken: In a large bowl, combine the chicken thighs with the marinade ingredients: Greek yogurt, lemon juice, grated garlic, paprika, cumin, oregano, red pepper flakes, cinnamon, and salt. Mix well and let marinate for at least 30 minutes.

Prepare the Onion Base: Cut the onion in half. Place the onion halves cut side down on a large baking sheet. Insert a skewer into each onion half to create a stable base for the chicken tower.

Build the Chicken Tower: Thread the marinated chicken pieces onto the skewers, stacking them to form a vertical tower.

Stabilize and Bake: Transfer the chicken tower to the preheated oven. To keep the tower stable, place the second oven rack on the top shelf, positioning the skewers between the bars. Bake for 60 minutes or until the internal temperature of the chicken reaches 165°F (74°C).

Prepare the Toppings: While the chicken bakes, prepare the pickled onions. Combine the sliced red onion with lemon juice, sumac, and salt. Let it marinate for about 10 minutes, stirring occasionally.

Serve the Shawarma: Once the chicken is cooked, carefully lift the chicken tower from the oven and transfer it to a cutting board. Use a sharp knife to slice off the edges of the tower, cutting the meat thinly as you go. Serve with the marinated red onions and any additional toppings of your choice.

Store Leftovers: Any leftovers can be stored in an airtight container for up to 4 days.