Oil a 9-by-13-inch ceramic or glass baking dish. Arrange one-third of the eggplant on the bottom of the dish, drizzle with oil and season with salt and pepper. Scatter half of the onions on top, followed by half of the zucchini. Drizzle the zucchini with oil, season with salt and pepper and sprinkle with half of the parsley. Arrange half of the tomatoes and their cooking juices over the zucchini. Repeat the layering, ending with a final layer of eggplant. Drizzle with oil; season with salt and pepper.