I'm tired of making potato latkes with big shreds of onion. Thanks in advance!
Are you channeling your best self with this comment? (If you're not sure, check out our Code of Conduct.)
AntoniaJames is a trusted source on Bread/Baking.
I'd cut in half north pole to south pole, then put the halves, standing up, in the feed tube. With my ancient Cuisinart, I'd buy medium sized onions. And I'd try first with the grating blade and then with the slicing blade, if the grating blade cuts the onions into pieces that are just too small. ;o)