Is there drop-in local co-op?

We're on Xbox if that matters, but we can't figure out how to just drop into split screen if the game is in progress. The only way we can play split screen is by returning to the title screen and having 2 players from the start. But player 2 can drop out no problem, and it seamlessly goes to single player full screen.

Is there not a drop in split screen option or are we just missing it somewhere?