Preheat the Oven to 450 degrees F. In a 13x9x2-inch glass baking dish, toss the potato, sweet potato, carrots, bell pepper, 2 tablespoons of the oil, ¾ teaspoon of pepper, and ½ teaspoon of salt. Arrange the onion evenly on top, then top with the zucchini. Drizzle with 1 tablespoon of the oil and sprinkle with ½ teaspoon each of salt and pepper. Arrange the tomato slices over the zucchini. Drizzle with the remaining 1 tablespoon of oil and sprinkle with the remaining ½ teaspoon each of salt and pepper.