From https://en.m.wikipedia.org/wiki/Muffuletta

A traditional-style muffuletta sandwich consists of a muffuletta loaf split horizontally and covered with layers of marinated olive salad, salami, ham, Swiss cheese, provolone, and mortadella. Quarter, half, and full-sized muffulettas are sold..

The signature olive salad consists of olives diced with the celery, cauliflower and carrot found in a jar of giardiniera, seasoned with oregano and garlic, covered in olive oil, and allowed to combine for at least 24 hours.

A muffuletta is usually served cold, but many vendors will toast it