In a medium bowl beat egg white with a whisk; stir in bread crumbs, milk, and half of the dry salad dressing mix. Add turkey; mix well. (Reserve the remaining half of the dry salad dressing mix for Olive-Tomato Relish.) Shape turkey mixture into four 3/4-inch-thick patties.
Place patties on the grill rack directly over medium heat; grill for 14 to 18 minutes or until turkey is done (165 degrees F), turning once halfway through grilling.
Serve the burgers on pita bread rounds with Olive-Tomato Relish and feta cheese. Makes 4 servings.
In a small bowl stir together white wine vinegar, olive oil, and the remaining half of the dry salad dressing mix. Stir in tomato, cucumber, and kalamata or ripe olives. Makes about 1-1/3 cups.