Layered seasonal vegetables are baked until they are meltingly tender.
Preheat oven to 375 degrees. Heat 3 tablespoons oil in a large skillet over medium heat. Add leek and garlic, season with salt and pepper, and cook until soft, about 4 minutes. Spread in a 9-inch gratin or round baking dish.
Arrange vegetables on leek in slightly overlapping circles, alternating zucchini, squash, tomatoes, and eggplant.
Top with wine, 1 tablespoon oil, oregano, salt, and pepper. Bake 30 minutes. Drizzle with remaining oil. Bake until vegetables are tender, 30 minutes more. Serve with Parmesan.