In a bowl, combine the chicken thighs with the shawarma spice blend, cumin, paprika, cinnamon, salt, and pepper. Let it marinate for at least 10 minutes; if you have more time, marinating for up to 2 hours is ideal to allow the flavors to penetrate deeply.
In a large pot or Dutch oven, heat olive oil over medium heat. Add the sliced onions and sauté until golden brown, which takes about 5 minutes; this step builds a sweet base flavor that complements the spices in your dish.
Stir in the minced garlic after onions are ready and cook for an additional minute until fragrant; be careful not to burn it as burnt garlic can impart a bitter taste.
Now add your marinated chicken thighs into the pot. Cook them for about 5-7 minutes, turning occasionally until they are browned on all sides; browning locks in juices while enhancing flavor through caramelization.