Beef Kofta Kebabs with Tzatziki Sauce

Name: Beef Kofta Kebabs with Tzatziki Sauce
Ingredients: * 1 pound 93% lean ground beef; * 3 tablespoon grated or minced onion; * 2 clove garlic, grated or minced; * 1/4 cup parsley, finely chopped; * 1 1/2 teaspoon ground coriander; * 1 teaspoon ground cumin; * 1 teaspoon salt; * 1/2 teaspoon pepper; * olive oil, for brushing the grill; * flat bread, for serving (optional); tzatziki sauce:; * 1 cup plain nonfat fat or reduced fat greek yogurt; * 1/2 cup grated cucumber, squeezed dry; * 1 clove garlic, grated or minced; * 1 teaspoon lemon juice; * 1 teaspoon fresh mint or dill; * pinch of kosher salt