Combine egg and bread crumbs in a mixing bowl. Add onion, garlic, mint, cinnamon, salt, and pepper; mix well. Add ground meats; mix well. Shape into 1-inch balls.
Place in a 15x10x1-inch baking pan. Bake in a 350 degree F oven about 15 minutes or until done. Pat cucumber dry with a paper towel. Stir shredded cucumber into yogurt.
Transfer meatballs to serving plate. Garnish with cucumber and lemon slices. Serve with cucumber-yogurt mixture and, if desired, quartered pita rounds. Makes about 16 servings.