Tennessee Onions

Preheat oven to 350°F.
Coat a 9×13-inch baking dish with cooking spray.
Slice onions into ¼ inch thick rounds.
Spread onions in the baking dish.
Season with salt, garlic powder, and oregano.
Distribute butter pats over onions.
Sprinkle Italian blend, cheddar, and Parmesan cheeses over onions.
Bake for 35-40 minutes until cheese is browned and bubbling.
Serve warm.