In a large bowl, combine the Greek yogurt, olive oil, lemon juice, lemon zest, minced garlic, zaatar seasoning, kosher salt, black pepper, and red pepper flakes. Whisk until well blended.

Add the boneless chicken thighs or breasts to the marinade. Make sure each piece is fully coated. Cover the bowl and let it marinate in the fridge for at least 30 minutes.

While the chicken marinates, preheat your oven to 400°F (200°C).

Transfer the marinated chicken into a baking dish. Pour any remaining marinade over the top.

Bake the chicken for 30-45 minutes, or until it's cooked through and reaches an internal temperature of 165°F (75°C).

Once cooked, remove from the oven and garnish with freshly chopped parsley. Serve warm.