This baked riff on ratatouille may look sophisticated, but it's surprisingly simple. Serve it for brunch or at dinner parties -- and save leftovers to eat straight out of the dish by the forkful.
Heat oven to 375 degrees. Heat oil over medium and cook onion until tender and lightly golden, 6 to 8 minutes.
Arrange the onion on the bottom of a 9-by-13-inch baking dish. Overlap tomato, squash, and potato on top of the onion. Season with salt and pepper, sprinkle with thyme and Parmesan, and drizzle with more oil.
Bake covered for 30 minutes. Uncover and bake until golden, 30 minutes more.