Preheat the oven to 450°F and spray two large baking sheets with cooking spray.
In a medium bowl, whisk the cornstarch, milk, and hot sauce.
In a shallow bowl, combine the panko, Cajun seasoning, and garlic salt.
Dip each onion ring into the cornstarch mixture then dredge them in the panko. Lightly press the panko onto the rings so it sticks. Place the breaded onion rings in a single layer on the prepared baking sheets.
Bake the onion rings for 20 minutes or until the breading is golden and crispy.