1For the Chicken Souvlaki, mix 1/4 cup of the extra-virgin olive oil and Greek Souvlaki Seasoning in small bowl. Place chicken in large resealable bag. Add Greek Souvlaki Marinade to bag; turn to coat. Refrigerate at least 1 hour or overnight for more flavor. Remove from marinade. Discard any remaining marinade.
2Place oven rack 6 inches from broiler. Preheat broiler on high. Line shallow baking pan with foil. Place wire rack on pan. Arrange chicken in single layer on rack. Sprinkle with salt.
3Broil chicken 8 minutes or until browned and cooked through. Transfer to cutting board and let rest.
4Meanwhile, for the Tzatziki Sauce, cut cucumber in half lengthwise. Thinly slice one half of the cucumber; set aside. Shred remaining half of cucumber using large holes of box grater. Mix shredded cucumber, yogurt, olive oil, lemon juice, Greek Souvlaki Seasoning, salt and pepper in medium bowl. Refrigerate until ready to serve.
5Brush pitas with remaining 1 tablespoon olive oil. Place on wire rack on baking pan. Broil pitas until lightly toasted, about 1 minute.
6Divide chicken evenly among pitas. Top with romaine lettuce, red onion and sliced cucumber. Drizzle with Tzatziki sauce to serve.