1. Whisk olive oil, fresh lemon juice, minced garlic, dried oregano, cumin, smoked paprika, crushed red pepper flakes, salt, and pepper together in a medium bowl until well combined.

2. Add the chicken thighs to the bowl or a zip top bag, toss to coat in the marinade, cover, and refrigerate for at least 30 minutes and up to 4 hours.

3. Make the tzatziki by stirring together the Greek yogurt, grated and squeezed dry cucumber, lemon juice, olive oil, dill, minced garlic, salt, and pepper in a small bowl, then chill until ready to serve.

4. Heat a grill pan, cast iron skillet, or outdoor grill over medium high heat and cook the marinated chicken for 5 to 6 minutes per side, or until nicely charred and the internal temperature reaches 165°F.

5. Transfer the cooked chicken to a cutting board, let it rest for 5 minutes, then slice it into thin strips.

6. Warm the pita breads in a dry skillet, directly over a gas flame, or wrapped in foil in a low oven until soft and pliable.

7. Assemble each gyro by layering lettuce, sliced chicken, tomato, cucumber, red onion, and feta on a warm pita, then drizzle generously with tzatziki sauce, fold, and serve immediately.