In a large bag, combine the vinaigrette and chicken and marinade for 1 hour in the fridge.
Meanwhile, preheat your grill and oil grill grates.
Discard marinade and grill chicken until cooked, about 15-20 minutes. Remove from grill and slice into thin strips.
For The Cucumber Yogurt Sauce
In a small bowl combine the yogurt, cucumber, garlic, and lemon juice. Season with salt and pepper and chill until ready to use.
For The Sandwich
Prepare the sandwiches by filling the pita pockets with the sliced chicken, a bit of the cucumber yogurt sauce, and lettuce, tomato, and red onion.
Pack these pitas in your lunchbox for a healthy lunchtime meal.
The cucumber yogurt sauce can be made a day in advance.
Make lunch time fun by pairing this Greek Chicken Pita Sandwich with a bowl of Tomato Cucumber Chickpea Salad.