In a row, line up the bowls of onion rings, batter, breading mixture, and the prepared baking sheet. Dip an onion ring into the batter, coating it all over. Transfer the onion ring to the breading, tossing to coat. Use a clean, dry hand to sprinkle the breading onto the onion as needed. Place the coated onion ring on the baking sheet and repeat with the remaining ingredients, arranging the rings in a single layer. Use a second sheet if needed. You should have enough batter and breading for about 20 onion rings.