Preheat oven to 450F. Combine 1 teaspoon oil, 1 teaspoon garlic, the lemon peel, thyme and 1/2 teaspoon each salt & pepper in large bowl. Add chicken and onions; toss well to coat. Spread on jelly-roll pan and roast 40 minutes.
Meanwhile, in another bowl combine remaining 2 teaspoons each oil and garlic, 1 teaspoon salt and 1/2 teaspoon pepper. Add remaining vegetables; toss well. Spread on another jelly-roll pan. Halfway through roasting chicken, add vegetables to oven and continue roasting both pans 20 minutes more.