Position rack in top third of oven, the other in the center, and preheat to 425°F. Line two rimmed baking sheets with foil and spray or oil it.
Whisk 3 tablespoons of oil and a tablespoon each of thyme and marjoram in large bowl. Add yams, carrots, parsnips, rutabagas, and onions, and toss to coat. Sprinkle vegetables generously with salt and pepper and toss.
Add the trays to the oven and roast vegetables until tender and brown in spots, turning occasionally, about 50 minutes. Watch carefully and rotate the trays top to bottom, front to back as needed. If any are done before the rest, remove them and continue to roast the remaining.
Can be made 4 hours ahead. Let stand at room temperature, if comfortable with it. If desired, rewarm in 350°F oven about 15 minutes, or microwave on high until heated through, about 6 minutes, before continuing.
Whisk balsamic vinegar, remaining 3 tablespoons oil, remaining thyme and marjoram to blend in a small bowl. Drizzle over roasted vegetables. Sprinkle with chopped parsley and lemon peel. Season with more salt and pepper, if desired. Transfer to a platter and serve hot or at room temperature.