Place chicken into a zip-top bag. Add 5 teaspoons teriyaki sauce and marinate in refrigerator for 3 to 4 hours.
Dice onion; chop scallions, lettuce and tomato.
In medium frying pan heat 1 tablespoon oil and cook chicken thoroughly until no pink remains. Meanwhile, in a small frying pan, sauté onion in 1 tablespoon olive oil.
While chicken and onion are cooking, combine mayonnaise, scallions and 2 teaspoons Kikkoman® Less Sodium Teriyaki Sauce. Put mixture aside.
Cut each cooked chicken breast into several strips.
Take pita halves and coat inside with mayonnaise mixture. Fill pita with several chicken pieces; top with sautéed onion, lettuce and tomatoes.