Peel the onions and slice them into very thin rings about 1 to 2 millimeters thick using a mandoline or sharp knife.

Separate the onion rings with your fingers and spread them in a single layer on paper towels; pat thoroughly to remove as much surface moisture as possible.

Transfer the dried onion rings to a large bowl, drizzle with vegetable oil, and sprinkle with salt, garlic powder, and smoked paprika.

Gently toss the onions with your hands or a spatula until they are lightly and evenly coated with oil and seasoning.

Preheat the air fryer to 350°F for 3 minutes and lightly spray the basket with nonstick cooking spray.

Place the seasoned onions in the air fryer basket in a loose, even layer, leaving space between rings and avoiding tight clumps; cook in batches if needed.

Air fry at 350°F for 12 to 15 minutes, shaking the basket or tossing the onions every 3 to 4 minutes to promote even browning.

During the last few minutes, watch closely and remove any pieces that turn very deep brown so they do not burn.

When the onions are deep golden with slightly browned edges and feel crisp, transfer them to clean paper towels in a single layer and let them cool completely.

Once fully cooled, use immediately as a topping or store in an airtight container at room temperature for up to 2 days or in the refrigerator for up to 5 days.