The broadest general definition of a Sicilian is a pizza based on a thick, foccaccia-like dough baked in an oiled pan, usually at around 450 degrees. The authentically Sicilian version of this style is made with semolina flour and topped with tomatoes and breadcrumbs, with optional Caciovallo cheese and/or anchovies. The transnational version is made with standard pizza flour and topped with just about anything; in America, tomato sauce and mozzarella, in generous quantities, is typical. Sicilian pizza in all its expressions and variants is radically different from the Chicago deep-dish style.
JLP