With a meat fork, turn chicken and cook for an additional 4 minutes. Depending on thickness of the chicken breasts, you may need to finish cooking in the preheated oven for 3-5 additional minutes. With an instant read meat thermometer, check internal temperature. It should read 165 degrees Fahrenheit when cooked through. If transferring cast iron skillet to the oven to continue cooking, use hot pads when transferring to the oven. When chicken is done, remove from cast iron skillet and rest on a cutting board for at least 5 minutes for juices to redistribute. Note: If chicken rests in a hot, cast iron skillet, it will continue to cook. Slice. Fan sliced chicken over spinach dressed in lemon vinaigrette.