When I was interviewing for both junior and senior positions, my typical tack was to look through their resume and look for something interesting that I have some kind of background knowledge of. Or, alternatively, just ask them "what's the coolest project you've worked on?" From there I'd just let it be a pretty organic conversation where I'd just keep asking for more details until we've either gotten to the bottom of the tech implementation or have gotten to the point where they can say "I don't know, someone else worked on that".
So far I haven't been disappointed with any of the outcomes from that process; there was one where my conclusion was "no hire" and then down the road they were hired anyway... and it turned out pretty much how I figured it would. Good surface technical knowledge with a super scattered implementation.