Heat oven to 350 F and prepare a 9x13 dish with non-stick cooking spray.
Turning the onion sideways, slice into ¼ inch rounds and separate the rings.
Spread onion rings in baking dish and sprinkle with the salt, garlic powder, and oregano.
Slice the butter into approximately 8 pats and place evenly across dish.
Sprinkle the Italian blend and cheddar cheese over the onions and then add the parmesan on the very top.
Bake for 35-40 minutes or until cheese is starting to bubble and brown.
Serve while still hot!
3-4 sweet onions, we used Vidalia
4 tablespoons butter
1 teaspoon salt, or to taste
1 teaspoon garlic powder
1/2 teaspoon oregano
1 cup shredded Italian blend cheese
1 cup shredded cheddar cheese
½ cup shredded parmesan cheese