Following the grand tradition of the turducken, this dish is a sirloin steak, with a pocket cut into it, stuffed with oysters and skewered shut. Seems to be most popular in Australia, where it probably originated, although some claim it is a United States dish. I've never tried to cook it, but most recipes seem fairly straightforward; the main idea is that the juices meld together. In case that's not enough of a flavor clash, it's generally wrapped in bacon and served with vegetables. The name is apparently a metaphor for the dish itself, with the bag being the steak.
I'd never heard of this until today, when it was mentioned in the novel The Manchurian Candidate. If you've tried this, or are inspired by this write-up to attempt it, feel free to /msg me and lemme know.