Would be category 31, alternative fermentables beer - subcategory 31A, alternative grain beer... but listing it here as a English Barleywine to get the numbers in a similar ballpark (English Barleywine, or even Wheatwine - with oats instead of wheat, would be base style).

Bake half or all of flaked oats in oven if want to add a toasted oat flavor (just keep an eye on them - can burn easily).

I BIAB, so I’m not worried about a stuck sparge, but I’d add rice hulls if you are, with this much oats. The Beta-Glucanase rest helps reduce this as well.

Can use hops of your choice, but I’m aiming for British varieties... First Gold, Target, or Fuggles would also work.

Lots of options for yeast - want good attenuation and some fruity esters, so Kölsch or an attenuative English Ale yeast such as WLP007, Wyeast 1028 London Ale, 1098 British Ale, 1318 London Ale III, 1335 British Ale II, 1450 Denny’s Favorite 50, 1728 Scottish Ale, or other dry yeast equivalent. Grists with high percentages of oats have been shown to produce more diacetyl than barley, so slowly raise (2°/day) fermentation temp after 3-4 days active fermentation, to around 68-70 for a diacetyl rest.

Age on oak if desired. Cold crash and gelatin fine before packaging.