Preheat the oven to 425 degrees. Cover 1-2 baking sheets with parchment paper or spray with cooking spray. Most likely you will need two baking sheets so the rings don't overlap at all. Slice the onions into rings, about 1/2 inch each.
Mix together the flour and seasoned salt in a shallow dish. In another shallow dish, add the whisked egg whites and hot sauce. Place the breadcrumbs in another shallow dish. This is to create your breading station.
Dip the onion rings in the flour, then the egg whites letting any excess drip off, and then dip into the breadcrumbs. Place on the baking sheet in a single layer. You can speed this process up by adding the breading to a Ziploc bag and then adding the coated onions there. Shake the bag to coat. The coating won't be quite as even, but it is significantly faster.