1. To make the tzatziki sauce: In a small bowl, combine 1/2 cup lowfat plain Greek yogurt, 1/4 cup finely chopped seedless cucumber, the zest and juice of 1/2 lemon, and 1 grated garlic clove. In a medium bowl, toss 1/2 cup coarsley chopped cucumber, 1/2 cup chopped tomato, 2 oz. crumbled feta cheese, and 8 torn mint leaves.
2. Preheat a grill to medium-high heat and oil the grates. In a large bowl, mix 1 lb. ground lamb, 1/4 cup finely chopped red onion, 2 tsp. ground cumin, 1 tsp. ground coriander, and 1/4 tsp. salt. Shape the mixture into four, 1/2-inch thick oval patties. Grill, covered, 4 to 5 minutes per side, or until cooked through (160 degrees F).
3. Spread the tzatziki sauce in 4 whole-wheat pita pocket halves. Stuff with the patties and top with the cucumber salad.