Chicken Souvlaki

Ingredients

• 1 1/2 teaspoons finely grated lemon zest, plus 3 tablespoons fresh lemon juice
• 2 garlic cloves, finely grated
• 1 tablespoon chopped fresh oregano
• 2 tablespoons extra-virgin olive oil
• coarse salt and freshly ground pepper
• 1 pound boneless, skinless chicken breast halves, cut into 2-inch cubes
• 1/2 english cucumber, chopped
• 1/2 cup fat-free greek yogurt
• 3 plum tomatoes, quartered
• 1/2 small red onion, cut 3/4 inch thick, and separated into slices
• 4 whole-wheat pitas