I'm still a greenhorn here, but I see a few options.
Find a short lag bolt / screw that will fit the hole so that threads catch. Use silicon or dicor on the bolt before inserting. This way it's temporary and you can add the wires back if ever you wanted.
For a seamless fix, I'd say some fiberglass / bondo also on the backside to make a giant rivet, then sand / paint as needed.
I had some holes from moving exterior lights and switching to different sizes, but also didn't have days for a fiberglass patch. So I used some extra aluminum sheet I had, used dicor as a sealant around the edge , then used machine screws to attach , I then painted over it all. It's not as clean as it could be, but it works. No leaks thus far.