Step 1

Position racks in upper and lower thirds of oven; preheat to 450 degrees F. Coat 2 large rimmed baking sheets with cooking spray.

Step 2

Cut off both ends of each onion and peel. Slice into 1/2-inch-thick slices; separate into rings. (Discard the smallest rings or reserve for another use.) Place the rings in a medium bowl; cover with cold water.

Step 3

Combine flour and baking powder in a shallow dish. Lightly beat eggs in another shallow dish. Combine breadcrumbs and seasoning in a third shallow dish. Working with one ring at time, remove from the water, letting any excess drip off. Coat in flour, shaking off any excess. Dip in egg and let any excess drip off. Then coat in the breadcrumb mixture, shaking off any excess. Place on the prepared baking sheets. Generously coat the onion rings with cooking spray.

Step 4

Bake for 10 minutes. Turn each onion ring over and return to the oven, switching the positions of the baking sheets. Continue baking until brown and very crispy, 8 to 10 minutes more.