Place both baking sheets into pre-heated oven, with chicken on the upper rack. Roast for 20 minutes, then rotate both baking sheets and roast for another 15-20 minutes, or until an instant-read thermometer inserted into the chicken reads at least 165°F and the vegetables are tender and caramelized. (Depending on your oven and how thin you sliced the vegetables, they may be done a little sooner).