Preheat the dutch oven to 400 degrees. Finely dice the onion and mince the garlic. Saute onions in dutch oven with olive oil until softened (roughly 5 minutes) then add the garlic until fragrant (about 1-2 minutes).
While the onion and garlic are sauteing, thinly slice the rest of the vegetables using a mandolin. Slice them into the same shape.
Spread the softened onion and garlic in the bottom of the dish. Place the thinly sliced vegetables in the baking dish vertically, in an alternating pattern. Sprinkle generously with salt, pepper, thyme, and rosemary.
Cover the dish with foil and bake for 30 minutes.
Optional: Top with cheese and bake for another 15-20 minutes or until the cheese is golden brown.