Step 1: Preheat the Oven

Preheat your oven to 350°F (175°C). Lightly grease your baking dish with butter or non-stick spray.

Step 2: Slice the Onions

Peel your onions and cut them into ¼-inch thick rings. For uniform thickness, use a mandoline slicer. Separate the rings gently.

Step 3: Arrange the Onions

Layer the onion rings evenly in the baking dish. You can slightly overlap them for a more compact bake.

Step 4: Season Generously

Sprinkle the garlic powder, onion powder, oregano, paprika, salt, and pepper evenly over the onions. Toss lightly if needed to distribute the seasoning.

Step 5: Add the Cheeses

Sprinkle the shredded cheddar, mozzarella, and parmesan evenly across the onions. Make sure every slice is covered in cheesy goodness.

Step 6: Drizzle with Butter

Pour the melted butter over the top to help the onions caramelize and the cheese melt into a rich crust.

Step 7: Bake

Cover the dish with foil and bake for 30 minutes. Then remove the foil and bake for an additional 15–20 minutes, until the cheese is bubbly and golden brown.

Step 8: Garnish and Serve

Remove from the oven and let rest for 5 minutes. Garnish with fresh parsley or thyme if desired. Serve warm.