Generously season ribs all over with salt and pepper. Allow to rest one hour or overnight, uncovered and refrigerated.
Preheat oven to 325°F. Toast Panko breadcrumbs on a rimmed baking sheet until golden brown, 8–10 minutes. Let cool, set aside.
Add a cup of beef broth or water to add to the roasting pan. Place the ribs meaty side up in the pan, cover pan with aluminum foil and bake in oven until meat is tender, 2 1/2 to 3 hours.
While ribs bake mix garlic, parsley, horseradish, lemon zest and juice, breadcrumbs, and oil in a small bowl. Season gremolata with salt and pepper to taste. Set aide, covered, in the refrigerator.
Uncover the roasting pan and bump up the oven temperature to 400°F. Roast until ribs are browned on top, about 25 minutes longer.
Spoon the gremolata over the short ribs before serving.
Notes
If you can, use a Meyer lemon for the juice and zest. I prefer it for the lemon/orange essence.