Preheat oven to 450 degrees F. Lightly oil a baking sheet or coat with nonstick spray.
Place chicken in a single layer onto the prepared baking sheet. Stir in olive oil and seasoning mixture; gently toss to combine.
Place into oven and bake for 25 minutes, or until the chicken is completely cooked through, stirring halfway. Stir in lemon juice.
To serve, warm pitas in oven, about 4-5 minutes. Halve pitas, and fill with chicken, romaine lettuce, tomatoes, red onion, cucumber, feta and tzatziki sauce.
Serve immediately.
For the seasoning mixture
In a small bowl, combine garlic, oregano, coriander, thyme, cumin, cayenne pepper, cinnamon, 1 1/4 teaspoons salt and 1 teaspoon pepper.
Notes
Use a good quality sheet pan. A durable sheet pan is ideal – it will last for years with minimal wear and tear, and will help achieve even cooking and avoid warping at high temperatures.
Chicken thighs will be juicier. Thighs have a higher fat content than breasts, keeping the meat from drying out and allowing for better moisture retention even if they are slightly overcooked.
Slice first. Cut the chicken thighs into thin strips before baking as this mimics the thin-shaved texture of rotisserie meat. This allows the chicken to absorb the spice mixture and cook very quickly for maximum crispy, caramelized edges.
Avoid an overcrowded sheet pan. Avoid any overlap and arrange the chicken strips in a single layer for even cooking, to prevent steaming and to promote proper browning.
Make it Greek. Add crispy french fries right inside the pita with the other toppings.
Warm the flatbreads. Warm the flatbreads right in the oven while the chicken finishes cooking, serving warm with homemade tzatziki sauce for a complete meal.
Reheat in the oven. Leftover chicken can be rubbery when reheated. For best results with leftovers, reheat in the oven at 350°F, tightly covered in aluminum foil (with a splash of water or broth to prevent from drying out), until warmed through.