Step 1

Begin by preheating the oven to a temperature of 350°F (175°C). Subsequently, coat a 9x13-inch baking dish with a suitable non-stick cooking spray.

Step 2

After cleaning and peeling the Vidalia sweet onions, position them sideways and proceed to slice them into rounds that are approximately ¼ inch in thickness. Following this, it is necessary to separate the sliced rounds into individual onion rings.

Step 3

Next, arrange the separated onion rings uniformly across the base of the previously prepared baking dish. Once arranged, season the onion rings evenly with the salt, garlic powder, and oregano.

Step 4

The butter should then be cut into roughly eight even portions or pats. Distribute these butter pats evenly across the seasoned onion rings in the baking dish.

Step 5

Continue by uniformly sprinkling the Italian blend cheese and cheddar cheese over the arranged onion rings. Finish this cheese layering with a final topping of the shredded parmesan cheese.

Step 6

Once assembled, place the baking dish into the preheated oven. Allow the dish to bake for a duration of 35-40 minutes. The dish should be removed when the cheese has begun to brown and bubble.

Step 7

For optimal taste, it is advised to serve the dish promptly while it remains warm.