Preheat your oven to 450°F (230°C). While it heats, grab a large rimmed baking sheet and give it a light spray with cooking spray. This ensures that your onion rings won't stick and helps achieve a crispier finish.

In a medium mixing bowl, whisk together the egg whites, milk, and cayenne pepper. Make sure everything is blended well. This mixture will help the breadcrumbs stick to those onion rings beautifully, so take a moment to do it right.

In a separate bowl, place the panko breadcrumbs, adding a sprinkle of salt, pepper, garlic powder, and smoked paprika. Mix well, so the flavors are evenly dispersed. This is where the magic happens!

Using tongs, dip one onion slice into the egg mixture, ensuring it’s fully coated. Allow any excess liquid to drip back into the bowl. Then, gently place the wet onion into the bowl of panko and shake until it’s well covered. Don’t rush through this; the more even the coating, the better the crispiness will be!

After coating each onion ring, place it on the prepared baking sheet. Ensure they’re spread out with enough space in between them to encourage even baking. Repeat this process with the remaining onion slices.

Once all your onion rings are coated and arranged, give them a light spray of cooking spray one more time. This will help those breadcrumbs turn golden brown and crunchy. Now pop them into the preheated oven and bake for 12 to 15 minutes, or until they look crispy and golden. Keep an eye on them; you want that perfect crunch!