In a large bowl, combine the Greek yogurt, olive oil, lemon juice, minced garlic, smoked paprika, cumin, coriander, turmeric, black pepper, cayenne (if using), and salt. Whisk everything together until it's well combined and smooth.

Add the chicken thigh pieces to the bowl and toss them until every piece is thoroughly coated in the marinade.

Cover the bowl with plastic wrap and refrigerate for at least 4 hours, but for the best flavor, marinade overnight (up to 24 hours).

In a small bowl, combine the Greek yogurt, minced garlic, lemon juice, and olive oil. Stir until smooth.

Season with salt to your liking. If you're using fresh herbs, stir them in. Cover and refrigerate the sauce for at least 30 minutes to allow the flavors to meld.

Heat a tablespoon of olive oil in a large cast iron skillet or pan over medium-high heat.

When the pan is hot, add the chicken in a single layer (you may need to do this in batches to avoid overcrowding). Cook for 4 to 6 minutes per side, until the chicken is deeply golden brown and cooked through. You want to get a nice char on the edges.

If grilling, preheat your grill to medium-high. Thread the chicken onto skewers and grill for about 10 to 15 minutes, turning occasionally, until cooked through and with grill marks.

Let the chicken rest for a few minutes before serving. Serve with the prepared garlic yogurt sauce, warm pita bread, shredded lettuce, chopped tomatoes, and thinly sliced red onions.