Greek Chicken Burgers with Tzatziki Sauce

Name: Greek Chicken Burgers with Tzatziki Sauce
Prep time: 15 min
Total time: 15 min
Cuisine: Mediterranean
Ingredients: 1 medium peeled or unpeeled cucumber; 1/2 cup plain Greek yogurt (from 6-oz container); 2 tablespoons chopped onion; 2 teaspoons chopped fresh mint; 1 lb lean ground chicken; 1 cup chopped fresh spinach; 1/4 cup chopped pitted kalamata olives; 1 tablespoon cornstarch; 1 tablespoon chopped fresh oregano leaves; 2 cloves garlic, chopped; 1/4 teaspoon salt; 1/4 teaspoon pepper; 2 whole-grain pita breads (6 inch), cut in half to form pockets; 1/2 cup chopped fresh tomato