Greek Chicken & Cucumber Pita Sandwiches with Yogurt Sauce
Tip: To oil the grill rack, soak a paper towel with vegetable oil, hold it with tongs and rub it over the grates. (Do not use cooking spray on a hot grill.)
To make ahead: Refrigerate yogurt sauce (Step 2) for up to 2 days. For leftover sandwiches, prepare through Step 4, but only assemble what you'll eat immediately. Store the leftover sauce, sliced vegetables, and grilled chicken separately and assemble just before serving for lunch or dinner the next day.