The chicken parm hero is a New York pizzeria sandwich, and that lineage decides everything about it. It is not built at a deli counter from cold parts; it comes out of the same kitchen that makes the pies, using the same marinara, the same low-moisture mozzarella, and the same oven. The hero is the New York name for the long roll, and here the roll is a length of crusty Italian bread that can stand up to a saucy, molten filling. The defining thing is that the chicken parm hero is the plated chicken parmigiana, off the menu, moved onto bread and finished in the pizza oven rather than reheated.
The craft is a structural defense of a fried crust against three wet attackers. A breaded cutlet is fried for a hard, craggy shell, then it has to survive marinara, melted mozzarella, and the steam they throw off inside a closed sandwich. The New York build manages this with the roll and the oven. The crusty Italian loaf is chosen because its interior can take sauce without going to mush the way a soft roll would, and it is often warmed or briefly toasted so its face seals. The marinara is kept thick so it clings to the cutlet instead of running into the bread, and the mozzarella is laid against the chicken so it binds the stack as it melts under the oven's top heat. The cutlet's crust is the only texture in an otherwise soft sandwich, which is why every other decision exists to keep it from steaming itself limp. Timing at the lunch rush is the whole craft: fired hot and handed over fast, the hero holds its edges; left to sit, it slumps.
The variations stay in the same oven. The veal parm hero swaps the cutlet for pounded veal; the eggplant parm hero runs it meatless with fried eggplant; the meatball parm shares the roll and the bake with a different filling. The chicken parm grinder is the identical sandwich under New England's name and on New England's softer roll, a regional distinction that earns its own treatment. Each of those is a codified build with its own rules, and each deserves its own article rather than being crowded in here.