That's a tough one. I think I would accept it and open the door, get beautiful logs of birch and stack them to fill the gap, then paint the door inside and out and add a visible handle. I would paint them a brown that is close in color as the mantle and then I'd look for a new insert.

Thank you, Yayagal! I had been looking at custom metal/glass screens but your suggestion for a new insert prompted me to dig around. It looks like inserts might be more cost effective than just buying a custom screen, as the former would provide more efficient heating (so they claim) plus they'd already come with a screen. As for the wood locker, inside is just raw brick. We had it cleaned once but I think it's beyond our capabilities to open up. I think I'm seeing some tiling in my future.

I was thinking a big fluffy plant. :)

What about a very LARGE screen that covers the whole thing, firebox to wood box? You could still have an insert behind it.

What about using Faux Tin Ceiling Tiles cut to fit the flat part of the door then painted to match.