Preheat an outdoor grill for medium-high heat and lightly oil the grate.

Combine turkey, bread crumbs, spinach, Greek dressing, feta cheese, onion, egg, salt, and black pepper together in a bowl; form into patties.

Cook turkey burgers on preheated grill until no longer pink in the center and the juices run clear, 5 to 10 minutes per side. An instant-read thermometer inserted into the center should read at least 165 degrees F (74 degrees C).