2-3 Vidalia, or other sweet, Onions
1/2 stick Unsalted Butter
Garlic Salt and Pepper, to taste
1 Cup Cheddar Cheese, shredded
1 Cup Mozzarella Cheese
1/2 Cup grated Parmesan
Fresh Oregano, for garnish (why?)

 Using non-stick cooking spray, prepare a 9x13 baking dish. Heat oven to 350.
 
Slice the Vidalia onions in 1/4 to 1/2 inch slices and separate the rings.  Lay the rings in the prepared baking dish.  Sprinkle the onion rings with garlic salt and pepper.
 
Cut the butter into pats and place around the dish on top of the onions.  
 
Spread the cheddar and mozzarella cheeses on top of the onions and then top with the grated parmesan cheese.  Bake at 350 uncovered for 30 minutes or until bubbly and the cheese has started to brown (browned cheese bits is one of the best parts!)
 
Remove from the oven, allow to cool for a few minutes, garnish with some fresh herbs (oregano, chives, thyme all work well)  and then serve.