When I hear "oatmeal bar" I think of something like this.

That's what I would think of, too. Otherwise, I've never heard of an oatmeal bar. Sounds like a Scottish thing.
But what about people who don't like oatmeal? What were they supposed to do?

I never much cared for it, until I tried making it really thick, and eating it with butter and salt, the same way I like my grits.
None of that sweet stuff for me.