Carbonara.

I've been served this dish with peas, with onions and with cream.
I can forgive the bacon if it's really good bacon, as guanciale/pancetta can be hard to get here, but for gods sake don't ruin it with anything else.

I rarely order it when out because so many places just serve a generic dish with bacon and ham without mentioning it, and I am not being the snob that asks what they use.