Stir yogurt, lemon peel, and remaining egg whites into flour mixture. Stir gently with fork until mixture holds together. Turn onto lightly floured surface. Knead about 8 strokes to mix dough thoroughly. Pat out dough to form 8-inch circle. With sharp knife, cut evenly into 8 wedges. Arrange wedges, about 1 inch apart, on prepared baking sheet. Brush with reserved egg whites. Sprinkle with 1 tablespoon sugar. Bake 15 minutes, or until golden brown.