Where exactly did you use your basher?
I THINK the intended solution requires you to make a Lemming a climber, dig down the left edge of the OWW, bash right when you can. Let the Lemming drop and climb up the far wall, when he turns around up there, build left to the one way wall, mine down. Mine down again, have a Lemming build in the middle of the OWW (where you have) and build over to the exit. That essentially completes the route though you need to use the climbers at certain points to get them where you need them to be, but I THINK that is more or less what was intended. That's an impressive backroute though, I had mega trouble just doing it any way I could. Hell, that looks simpler than the intended solution, which is what I'd be listing in my Walkthrough for this difficulty.