Vegetarian Greek Sandwiches

whole-wheat sandwich thins

nonfat Greek yogurt

balsamic vinegar

scant ¼ tsp dried onion flakes

black pepper

sugar (optional)

spinach or arugula

Roma tomato, sliced into ¼-inch thin rounds

half of a cucumber, peeled and sliced diagonally into ¼-inch thin pieces

crumbled feta cheese