01 -
Preheat oven to 350°F. Ensure oven rack is positioned in the center.
02 -
Lightly coat a 9×13-inch baking dish with non-stick cooking spray for easy release and cleanup.
03 -
Peel Vidalia onions and slice crosswise into 1/4-inch thick rounds, keeping rings intact for structural integrity.
04 -
Evenly lay onion rounds across the base of the prepared dish. Sprinkle evenly with salt, garlic powder, and dried oregano.
05 -
Arrange butter pats over the surface of the seasoned onions for even melting and flavor.
06 -
Evenly sprinkle Italian blend cheese and cheddar cheese over the onions. Top with a final layer of Parmesan cheese.
07 -
Place baking dish in oven and bake for 35 to 40 minutes, or until cheese is melted, golden brown, and bubbling, and onions are fork-tender.
08 -
Remove from oven and let cool slightly before serving warm.