Preheat your oven to 425°F (220°C) and line a large baking sheet with parchment paper or aluminum foil for easy cleanup.

In a large bowl, whisk together the olive oil, minced garlic, ground cumin, coriander, smoked paprika, turmeric, kosher salt, and black pepper.

Add the sliced chicken thighs and red onion to the spice mixture, tossing thoroughly until the meat and onions are completely coated.

Spread the marinated chicken and onions in a single, even layer on the prepared baking sheet, ensuring they aren't overcrowded.

Roast in the preheated oven for 20 to 25 minutes, tossing halfway through, until the chicken is fully cooked and the edges are crispy and deeply browned.

While the chicken is roasting, prepare the sauce by whisking together the Greek yoghurt, grated garlic, lemon juice, chopped dill, chopped mint, and a pinch of salt in a small bowl until smooth.

To serve, warm the pita breads slightly, then load them with the hot chicken shawarma and drizzle generously with the homemade garlic herb yoghurt sauce. Enjoy immediately with crisp lettuce and diced tomatoes if desired.