The spiedie sub takes Binghamton's skewer sandwich and rebuilds it as a full long-roll construction, and the change of bread changes what the sandwich is. The marinated, fire-grilled cubes of chicken, pork, or lamb are the same, but instead of dropping off a skewer into a folded slice of soft bread, they are loaded the length of a split sub roll alongside grilled onions and peppers. The plain spiedie is meat and almost nothing else; the spiedie sub is a layered build that treats the marinated cubes as the protein in a proper hero rather than as the entire event. The defining decision is the roll: a sturdy split loaf turns a spare grill sandwich into a stacked, dressed, two-handed meal.
The craft is in the marinade and in making the roll carry a heavier load. The cubes still sit in the sharp vinegar-and-oil dressing long enough for the acid to tenderize them through, and they are grilled hard so the edges char while the centers stay juicy. Onions and peppers are cooked down soft and sweet on the same fire or flat-top, where they do structural work as well as flavor work: they add moisture, sweetness, and a yielding layer that fills the roll around the firm cubes so each bite holds meat and vegetable together. The roll has to have a crust with enough structure to carry that wet, charred, oily filling the length of the sandwich without folding in the middle, which is exactly the engineering the wider sub family is built on. Extra marinade is brushed on rather than poured, so the bread is seasoned without being drowned.
The variations track the meat and the dress. Chicken is the common build, with pork and lamb the older readings, each taking the marinade differently; some shops add provolone or a hot pepper relish to push it further into hero territory. Stripped back to a single slice of soft bread and the bare skewer it returns to the plain spiedie, and the long-roll family it sits in here, the hoagie, the hero, the grinder under their regional names, runs on its own founding rules, and each of those deserves its own article rather than being crowded in here.