Let the junior handle it
There are a certain range of parts/cogs/tubes/solutions a programmer will always be creating and recreating. Solutions such as login functionality, file storage functionality, basic resource editing, continuous integration, logging setup etc. And when tasks such as these have become rote routine and quick to do it's time to let someone less experienced handle them.
That's an insight I gained from a podcast on programming. One of the podcast guests noted that if the task was very familiar and easy to do (for that person) they would let someone less experienced with the task handle it instead.
It won't be fast and it might even be error prone. But it's a good knowledge transfer process since you will have an easy time mentoring because you'll be very familiar with the task. And who knows maybe you'll get a new perspective on how to solve the task? :)
Photo credit: Julian Montoya (Licensed under CC-BY-SA).