I'm not sure there are any 5e one-shot adventures! Certainly, WotC's published adventures don't fit the bill, and I think even the third-party stuff is aimed at multiple sessions.
You might try taking a chapter out of "Lost Mine" and running with that, or perhaps one of the intro scenarios from PotA (I haven't got to that yet, so can't comment on quality). Or perhaps you could snag something from the Adventurer's League, perhaps (again, you'll need someone else to make a recommendation).
Beyond that, your options seem two-fold: either homebrew (which shouldn't be too bad), or convert. Perhaps one of the Free RPG adventures, from WotC or Paizo or someone else, might suit? ("We be Goblins" is great, but then you'd need to convert the pre-gen PCs too.)