This is one of the best sandwiches I've ever made.
It helps that I smuggled back a jar of Il Primo giardiniera from Chicago.
Slice a good baguette in half, and remove most of the fluff. Spread one side with mustard, or better yet, Trader Joe's Aioli Garlic Mustard Sauce. Top with a slice of provolone. Put 2 slices (or 4, if you're feeling especially porky) of mortadella on the other half. Stick both halves in your oven and turn it on to 350. Let the cheese get melty and the bread get toasty. Put giardiniera on top of the cheese. Assemble, smoosh together, and eat.