As a coach at Mochary Method (which I know is coming from a biased perspective, so please take it with a grain of salt), I think the important thing to emphasiz

As a coach at Mochary Method (which I know is coming from a biased perspective, so please take it with a grain of salt), I think the important thing to emphasize here is having the conversation with your senior engineer first. In some situations, the senior engineer may love training and can allocate some of his/her time to up-leveling junior engineers. In other situations, the senior engineer may like to do 1:1s, but hates building the system/curriculum to train others. Find the win-win that meets both of your needs. As a general rule of thumb, it's best to keep every member of the team in their zone of genius (i.e. high competency AND enjoyment) as much as possible. Have the conversation so you can optimize for that.