I think you will like this.

I use oatmeal as filler

Without it, sounds like bread pudding to me!

I will predict it will taste exactly like meatloaf, salty meatloaf but meatloaf.

No matter what you put into meatloaf, it tastes consistently like meatloaf.

that calls for chunks of Swiss cheese. Haven't tried it, though I keep thinking I should some day. I'd think the mushroom soup (aside from the high sodium) would make it too moist, unless there was some starch in the mix.

My go-to meatloaf recipe is about a pound and a half of mixed ground meats - beef, lamb, pork, turkey, whatever the store has on sale - mixed with a cup or so of mirepoix, an egg, and enough breadcrumbs to make a coherent mix (it helps to have an assistant to pour in the breadcrumbs while I mix with my hands).

she'd put a layer of it in between layers of beef mixture

I imagine it was a way to stretch the meatloaf... she was always working on a budget.

You didn't mention how much ground meat you were using.

I have somehow never mastered meatloaf. During the years when I had kids at home, I'd periodically make it, but it was never very good.

Turkey, on the other hand, is astonishingly easy. I'd make it every other month or so, sometimes in the middle of the week. My kids would come home from school to a turkey dinner. Recently I asked one of them if he remembered that, and he did, quite fondly.