Carefully pick through the crab meat for any shells, sifting gently to keep the large lumps intact. Discard any shells.
Whisk together the egg, green onion, mayonnaise, parsley, Dijon mustard, butter, Worcestershire sauce, Old Bay seasoning, and cayenne pepper in a large bowl. Stir in ½ cup of the bread crumbs and mix well. Gently fold in the crab meat with your hands or a spatula, mixing without breaking up the crab lumps.
Shape the mixture into 6 equal patties, about ½ cup each. Crush the remaining ½ cup Panko into a fine crumb then dredge the patties, patting gently to cover. Cover and refrigerate the patties for 30 minutes up to overnight to firm up.
Preheat the oven to 375°F. Heat the oil in a large non-stick, oven-safe skillet over medium heat. Carefully place the crab cakes in the skillet and cook until browned, about 2 minutes. Gently flip and cook the other side for 2 minutes. Transfer the skillet to the oven and bake for 8-10 minutes.
Serve with a squeeze of lemon and tartar sauce.