Combine zucchini and onion in medium saucepan, add water to cover and bring to boil for 5 minutes. Drain and cool. Combine carrots, soup, sour cream and garlic powder in large bowl. Add zucchini, onion and chicken. Mix and spread in 9 x 13 inch pan. Mix stuffing mix and seasoning packet. Toss well and sprinkle over casserole. Top with cheese and bake covered for 45 minutes at 350 degrees for until golden brown.