In a large bowl combine the ground turkey, crumbs, onions, garlic, parsley, egg yolk, worcestershire sauce, salt, and pepper; mix until just combined. Do not overmix.
Form mixture into four flat patties. If the mixture is too wet to the point of falling apart, add a little more crumbs, or until desired consistency. Keep in mind, though, that the burgers should be wet and soft, and will firm up in the fridge.
Transfer the turkey burgers to a large plate and then place them in the refrigerator for about 20 to 30 minutes.
Remove the burgers from the fridge.
Preheat the grill to high; about 425˚F to 450˚F.
Oil the grates.
Using your thumb, create an indent in the center of each turkey patty.
Transfer to the grill and cook for 6 minutes; flip over and continue to cook for 5 to 7 more minutes, or until internal temperature of the turkey burgers registers at 160˚F to 165˚F.
Remove from grill and let rest for about 5 minutes before serving.