Heat oven to 350°F. Spray 8 regular-size muffin cups with cooking spray.
In medium bowl, mix meat loaves ingredients. Scoop generous 1/3 cup meat mixture into each muffin cup, pressing down slightly.
Bake 30 to 35 minutes or until meat thermometer inserted in center of one loaf reads 160ºF. Let stand in pan 5 minutes.
Meanwhile, in small bowl, mix tzatziki sauce ingredients; refrigerate until serving time. Serve meat loaves with tzatziki sauce.