Mix together all ingredients, except hamburger buns, until combined. Form mixture into 5 patties, about 3/4 inch thick. Grill over medium-high heat until browned on both sides, turning burgers once (resist the urge to press down on the burgers while they are grilling). Burgers are done when the internal temperature registers 165 degrees F on a meat thermometer. Serve on toasted buns with lettuce, tomato, and cheese if desired.
