What Was That Volunteer Squash Thing?

We had the volunteer squash thing last night for dinner.  It was awful - no flavor despite butter and pepper and butter and cinnamon, I tried it both ways.

Cutting it in half was a task that required muscle.  The skin was very firm and I had to pound it with the knife in the cut to go through it.

I scooped out the seeds and baked it open side down for an hour. Then turned it over and sprinkled one half with pepper and one half with cinnamon.  It looked like an acorn squash.  But taste-wise was so bland.  Neither of us finished our serving and it went into the compost bin.

Lesson learned?  Don't nourish any volunteer squash types no matter how prolific they grow!