Hey! I ate this!
This type of sandwich is said to have its roots in the Jewish community of medieval Palermo. A soft bun is stuffed with bits of beef spleen and beef lung which are first boiled and then fried in a little bit of lard. This one has a topping of shredded caciocavallo cheese and fresh ricotta under the meat.
This and other local snack specialties were had at L'Antica Focacceria de San Francesco in Palermo, and was said to be a more upscale version of a rough treat suitable for 'sailors or ruffians'.