Combine all ingredients (may allow mixture to sit overnight in the refrigerator to improve flavor).
Preheat gas grill to medium high.
While the grill is heating up, remove meat mixture from refrigerator if prepared ahead, and form into 4 patties.
Grill patties about 4 minutes per side for or until the internal temperature is 145 degrees.
Top with lettuce, tomato, onion, and tzatziki sauce and serve on a hamburger roll.