How to help mid-level engineers increase their cognitive capacity

I’m working on a fairly bloated monolithic codebase, with a medium amount of technical debt and bad architecture choices. The development team consists of 3 senior devs (15+ YoE) and 3 mid-level devs. The seniors are doing fine, but the mid-level devs often seem to get overloaded by the solution space.

We are introducing DDD to try and reduce the overall cognitive load when working with the code, but I am also looking into growing my mid level devs in a way where they won’t get lost as often and as quickly in the code.

I kind of learned how to do that on my own, over time, so I’m struggling a bit with coming up with ways of guiding and helping them mature faster. Do you all have any tips or tricks in that regard?