Cut the chicken breasts in half lengthwise. Then cut in half. If you are using thighs you can simply cut lengthwise.* Sprinkle each side with salt and pepper. If desired put back in the fridge for up to 4 hours. This will help hold more of the moisture in.
Heat a large cast-iron skillet over medium heat. Once you feel the heat radiating from the skillet, add the oil and swirl it around until the surface of the skillet is covered. Add a few pieces of chicken at a time. Don't overcrowd the skillet. Cook for about 3-4 minutes per side. You want the chicken to be lightly brown on the bottom before you flip it over
Continue to cook the remaining chicken. Cut one piece of chicken to ensure that it is cooked through. Set aside and allow the chicken to continue to rest for about 5 minutes before slicing.
*Instead of slicing for slightly thinner chicken, you can pound the chicken flat. For chicken breast slice in half, thighs can be left whole. Then place the chicken between parchment paper and pound with the flat side of a meat mallet until they are a 1/4 inch thick.
Recipe by Nourishing Simplicity at https://nourishingsimplicity.org/how-to-make-pan-seared-chicken-breast-or-thigh/