The spiedie is a Binghamton sandwich whose bread does almost nothing, and that is the whole design. Cubes of chicken, pork, or lamb are marinated for a day or more in a sharp, herby, vinegar-and-oil dressing, threaded onto a skewer, and grilled over fire until the edges char. The sandwich is assembled at the grill in one motion: a plain slice of soft Italian bread is folded around the hot skewer, the bread clamped down, and the meat pulled off so the cubes drop straight into the fold. There is no roll, no sauce poured on, no build. The bread exists to grip the skewer and protect the hand, and the marinated, fire-charred meat is the entire sandwich.
The craft is in the marinade and the pull. The cubes sit in the dressing long enough for the acid to penetrate and tenderize all the way through, which is why a properly made spiedie is juicy in the center despite a hard char outside; a short soak leaves it dry and one-dimensional. The meat is cubed small and even so it cooks fast and takes smoke and color on every face. The bread is deliberately soft and plain, a single slice rather than a split roll, chosen to be a neutral wrapper that absorbs the marinade's drip and gives the fingers purchase to strip the skewer clean in one tug. Any extra dressing is brushed on as the meat comes off the fire, not ladled into a built sandwich, because the point is the marinated meat itself, eaten hot off the stick, not a layered construction.
The variations are mostly about the meat and the dressing, since the form is so spare. Chicken is the common version now, but pork and lamb are the older readings and each takes the marinade differently. Local cooks guard their dressing recipes, and the balance of vinegar, oil, garlic, and herb is the argument. Built up on a long roll with onions and peppers it becomes the heartier spiedie sub, and the wider long-roll family it joins there, the hoagie, the hero, the grinder, runs on different rules entirely, and each of those deserves its own article rather than being crowded in here.