I just cleared Breakheart Banks of some nasty super-mutants.

This looks like a great place for a new settlement. Crops and defenses are already in place.

The only problem is: there's no workbench as far as I can tell.

Is there anything I can do at this point?

not sure where this is, but i've come across a place like this, was near another settlement and was what looked like a little settlement place run by mutants, but once i cleared them out i looked around for a while for a workbench and couldn't find one xD...it said the usual [cleared] on the map so dont think its a build spot

Some farms are not your farms. I found some empty store stalls like the kind you can build in some buildings in a city area. Couldn't find a box or anything but looked like it was going to be a market or another town.

Nope.

It doesn't seem like it is a place for you to build a settlement. Perhaps a future DLC will make it so... or a mod...