The guastella is a western-Sicilian street sandwich defined by the fryer it is built around, not by anything raw that goes into it. A soft, slightly sweet sesame roll, close kin to the Palermo vastedda, is split and loaded straight from the hot work in front of the seller: spleen and lung that have been simmered and then finished in lard, sometimes a spoon of ricotta, a fistful of shaved caciocavallo. The roll is plain on purpose because everything interesting has already happened in the pot and the pan. The defining move is that the bread meets a filling that is hot, fatty, and just cooked, and is eaten in the few minutes before either of those facts changes.
The craft is the dressing decision and the timing. The offal is kept glossy with lard hot enough to coat without turning the crumb to a sponge, and the roll is soft enough to compress around a loose filling rather than fight it. Eaten schietta, plain with a squeeze of lemon, the sandwich reads sharp and lean; eaten maritata, married with ricotta and caciocavallo, the cheese rounds the iron edge of the spleen and the fat carries it longer. Salt and lemon are worked in to order at the stall. None of it keeps: the guastella is handed over and eaten standing, because a roll that has waited has gone slack and the lard has set.
The named turns stay on the same street and the same vat: the plain lemon version against the cheese-married one, and the wider Palermo family of pani câ meusa and the panelle and crocchè rolls that run on the identical logic of a fryer or a pot poured into soft bread. Each of those is a different load in the same kind of roll, and each deserves its own article rather than being crowded in here.