Since I’m in Florida, I don’t know about Oregon, in particular, but the main thing would be that all of the cooking would have to be done in your home kitchen. That means that, unless there is something specific against frying, you may fry the doughnuts AT HOME, then package them and sell them at, for example, a farmers market. You would NOT be allowed to fry them at the farmers market.
Also keep in mind that any samples would have to be cut and packaged (e.g. in small cups with lids) at home and you would not be allowed to break doughnuts apart as samples at the market – only the home-packaged samples would be allowed.
Again, remember, I’m in Florida and the rules may be different in Oregon, but these are relatively common constraints.
This is an old post, but in case anyone else is wondering… it looks like Oregon requires you to have a domestic kitchen license (not a cottage industry license) to sell donuts. https://forrager.com/law/oregon-domestic-kitchen/ Check out ‘laws’ tab on this website to explore what is allowed under each type of license in Oregon. Cheers!