Combine zucchini, 1 cup bread crumbs, onion, eggs, butter, parsley, and seafood seasoning in a bowl; mix until well combined.
Form mixture into 4 round cakes. Pat remaining bread crumbs onto both sides of the cakes and transfer to a sheet of waxed paper. Refrigerate for 30 minutes.
Heat oil in a large skillet over medium heat. Fry chilled zucchini cakes until browned, 7 to 8 minutes per side. Drain on paper towels before serving.