In a medium bowl, combine all ingredients until blended. Sauce may be made up to 2 hours in advance. Cover and refrigerate until serving. The longer it has to meld flavors, the better.
For the wrap:.
Flatten breast to about 1/2-inch thickness. Place chicken breast in a plastic bag and add Italian dressing. Let the chicken marinate for at least 15 minutes, preferably longer; remove chicken. Lightly season with salt and pepper.
In a large non-stick skillet over medium heat, cook chicken breast about 5 minutes per side or until nicely browned and cooked through. Place chicken on a cutting board and slice thinly against the grain; set aside.
Warm pitas in microwave oven 30 seconds. Place one pita on a plate and spread 1/2 cup of the lettuce and 1/4 of the chicken slices on top. Sprinkle 1/4 each of the tomato, onion, Feta cheese and olives. Spoon some of the herb sauce over top and fold in edges of pita. Repeat with remaining pitas. Serve immediately with additional sauce on the side.
Serving Suggestion: Wrap sandwich in parchment or waxed paper for plating and serving.