The defining sensation of a panino con peperoni cruschi is the shatter. Peperoni cruschi are the sweet Senise peppers of Basilicata, strung up and sun-dried whole until they are leathery, then dropped into hot oil for a few seconds where they puff and crisp into something between a crisp and a leaf. The word crusco in Lucanian dialect means crunchy, and that crunch is the entire reason the sandwich exists. These are not stewed peppers softening into a filling; they are a brittle, sweet, smoky thing that breaks apart in the mouth, and the panino is built to preserve that fragility rather than smother it.
The craft is protecting the crisp from the moment of frying to the moment of biting. The peppers are fried fast and very briefly, because a second too long turns sweet to burnt and bitter, then drained and used while still rigid; once they sit against anything wet they go limp and the point is gone. The bread is plain and is kept dry on the inside, no sauce that would soften the pepper, sometimes the peppers crumbled in shards rather than laid whole so the shatter is distributed through every bite. The natural partner is something with a little fat to carry the sweetness without dampening the texture: a slice of mild cheese or a smear of soft pecorino, added so it sits beside the pepper rather than soaking into it. Restraint here is structural, not stylistic. It is eaten quickly, while the crunch still holds.
The variations are Lucanian and keep the crisp central. There is the version with the local cheese, the one over a fried egg whose richness frames the smoke, and the build crumbled onto bread with nothing but oil so the pepper is the whole statement. Each is the same shattering dried pepper met by one thing that does not wet it, and each deserves its own article rather than being crowded in here.