Step 1

Oven Preheating: Initiate the process by preheating the oven to 350°F (175°C). Concurrently, prepare a 9×13-inch baking dish by coating it evenly with a non-stick cooking spray.

Step 2

Onion Preparation: Post cleaning and peeling, position the Vidalia onions on their sides. Proceed to slice them into rounds of approximately ¼ inch thickness.

Step 3

Separation of Onion Rounds: Post slicing, each round should be delicately separated into individual rings.

Step 4

Arrangement and Seasoning of Onion Rings: Lay the separated onion rings flat within the pre-coated baking dish. Follow this by evenly distributing the salt, garlic powder, and oregano over them.

Step 5

Butter Application: Divide the unsalted butter into approximately eight equal parts or pats. These should then be evenly placed atop the seasoned onion rings.

Step 6

Cheese Layering: Commence by evenly sprinkling the Italian blend cheese, followed by the cheddar cheese over the onion rings. Conclude this step by topping it with the finely shredded parmesan cheese.

Step 7

Baking Process: Transfer the baking dish into the preheated oven. Allow it to bake for a duration of 35 to 40 minutes, or until the cheese on top begins to brown and bubble.

Step 8

Serving: It is recommended to serve the dish promptly while it is still warm to ensure the best flavor and texture.