In a large mixing bowl, whisk together olive oil, red wine vinegar, minced garlic, dried oregano, ground cumin, smoked paprika, salt, and pepper until well combined. Add the boneless, skinless chicken thighs to the bowl, ensuring they are well coated with the marinade. Cover with plastic wrap and refrigerate for at least 1 hour, or overnight for best flavor.

While the chicken marinates, prepare the creamy tzatziki sauce by combining Greek yogurt, grated cucumber, minced garlic, olive oil, fresh dill, lemon juice, and a pinch of salt in a medium bowl. Mix until smooth. Chill in the refrigerator for at least 30 minutes.

Preheat your grill or skillet to medium-high heat. Remove marinated chicken from the refrigerator and let it come to room temperature for about 10 minutes. Grill the chicken for 5-7 minutes on each side until cooked through and charred, or bake in a preheated oven at 400°F for 20-25 minutes.

Once cooked, let the chicken rest for a few minutes before slicing it into thin strips. Warm the pita bread on the grill or in a skillet for about 1 minute per side until soft.

Layer each pita with sliced chicken, tzatziki, halved cherry tomatoes, sliced red onion, shredded lettuce, and crumbled feta to assemble your gyros.

Drizzle with olive oil if desired and sprinkle with fresh parsley. Serve warm and enjoy!