In a large skillet heat your olive oil over medium high heat. Place your mushrooms, lemon zest, lemon juice and thyme into the pan. Cook for about 10 minutes, until the mushrooms have reduced in size and have become a nice golden brown. Make sure you stir the mushrooms every now and then.
Once the mushrooms are cooked, pour half of the chicken broth into the pan. Using a wooden spoon scrape the bottom of the pan to release all of the brown bits from cooking the mushrooms. Pour the mixture into a bowl, then cover and set aside.
Place the pan back on the stove over medium high heat. Pat the chicken dry and sprinkle each side with the salt and pepper.
Place the chicken into the hot pan and cook until the chicken reaches an internal temperature of 160°You will want to use a meat thermometer to check the temperature. Remove the chicken from the pan and place it onto a plate and cover.
Add the mushrooms back into the pan to create your sauce. Add the remainder of the chicken stock to the pan and use your wooden spoon to scrape up the brown bits from the pan.
Add the butter to the pan and cook the sauce down until the butter is completely melted. Pour any juices that might have accumulated on your chicken plate from the chicken resting into the pan.
Place chicken on a plate and pour the sauce over the chicken breast and enjoy.