Prepare Tzaziki Sauce (recipe, below). Over medium heat, brown crumbled sausage in a large, 10- to 12-inch skillet sprayed with cooking spray, flattening with spatula while cooking. Warm pita breads, one at a time in large skillet coated with cooking spray until lightly browned on each side. Repeat with pita, spraying skillet lightly with cooking spray between each. To assemble gyros, spread 2 or 3 tablespoons tzaziki sauce on each pita bread. Top with crumbled sausage, apple and onion pieces. Fold over.
Tzaziki Sauce: Combine 8 ounces sour cream, 1 cup peel of English Cucumber, diced, 2 tablespoons fresh lemon juice, 2 tablespoons chopped fresh mint and 1/4 teaspoon salt in medium bowl. Cover bowl tightly with plastic wrap and refrigerate until ready to use.
Note: If English cucumbers are not available, regular will be fine. For a reduced-fat version, substitute reduced-fat sour cream.