Italy doesn't have pizza. The modern dish, "Pizza", was invented in America. Hell, the deepdish was invented in Chicago at Pizzaria Uno.

So, pasta would be better attributable to Italy. But, if you're barring that route and looking for an inherently and uniquely American dish that doesn't ring of other countries' inspiration, the cheeseburger might answer the question. To make it easy though, you wanted something invented in America that is named after the American town it was invented in, go for the Philly cheesesteak.