Cut the chicken thighs into 1/2-inch wide strips. In a large bowl, whisk together 3 tbsp olive oil, lemon juice, minced garlic, cumin, smoked paprika, turmeric, coriander, cinnamon, cayenne pepper (if using), 1 tsp salt, and 1/2 tsp black pepper.

Add the chicken strips to the marinade, tossing to coat thoroughly. Cover the bowl and refrigerate for at least 15-20 minutes, or up to 2 hours for deeper flavor.

Preheat your oven to 400°F (200°C). Line a large baking sheet with parchment paper for easy cleanup.

In a separate small bowl, toss the bell pepper strips and sliced red onion with 1 tbsp olive oil, and season lightly with salt and pepper.

Spread the marinated chicken evenly on one half of the prepared baking sheet in a single layer. Arrange the seasoned bell peppers and red onion on the other half of the baking sheet, ensuring they are also in a single layer.

Bake for 20-25 minutes, flipping the chicken and vegetables halfway through, until the chicken is cooked through (internal temperature reaches 165°F/74°C) and the vegetables are tender-crisp and slightly caramelized. For extra crispiness, you can broil for the last 2-3 minutes, watching carefully to prevent burning.

Remove the baking sheet from the oven. Serve the chicken and vegetables immediately with warm pita bread, fresh chopped tomatoes, cucumbers, and a sprinkle of fresh parsley. Drizzle with Tahini sauce or garlic sauce, if desired.