If you are using a boneless skinless chicken breast your cooking instructions are a little different. You are going to start your vegetables in the 450 oven for 15 minutes, turn the temperature down to 400 and place your marinated chicken on the vegetables and cook for 12-15 minutes, checking it at the 12 minute mark. Once the chicken reaches 160 pull the pan from the oven (there will be carry over cooking and your chicken will rise to 165 out of the oven)