You can get proper breaded pork tenderloin sandwiches in Indiana, Missouri, and Iowa. You might think they're okay elsewhere, but they are not. An exception might be if someone from one of those places brought their cook and pigs to some other place, but not really.
We never got a breaded pork tenderloin during our recent road trip to Kansas City, because we ran out of eating room. So soon we're going to drive to Indiana for one.
There are two real kinds of pork tenderloin sandwich, and one of them is sort of a fancier version, of which I do not wholly approve. It is acceptable, but I'm not driving two hours for that kind.
It's properly served in a plastic basket lined with paper, and accompanied by french fries, onion rings or potato chips, and/or sometimes a little disposable cup of cole slaw, and also sometimes a pickle spear. But it's okay if it's on a plate these days, instead. People don't seem to go in for plastic basket lunches like they used to.
The pork tenderloin circumference should be several times the size of the bun, and it should be hand-breaded or at least coated in bread crumbs.
This also looks okay.
Sometimes people make them thicker so that they are not as big around, and use a batter, instead. I don't think that's right, but it can still be a good sandwich that way.
If it's Sunday, you can eat it with gravy and mashed potatoes and green beans, instead of on a bun. I guess. You're really just eating pork schnitzel at that point, aren't you?
But if you go to a place where they have breaded pork tenderloin which is formed into a neat round patty, don't order that.