While the fettuccine is cooking, heat the oil in a large skillet over medium heat. Season the chicken with salt and pepper on both sides. Add the chicken to the skillet and cook about three to four minutes on both sides or until an instant read thermometer inserted in the thickest part of the chicken registers 165 degrees. Remove the chicken from the pan, tent with foil, and set aside.
Without cleaning the skillet, add the butter to it and melt completely. Add the mushrooms to the pan, and cook until soft and tender. Add the spinach to the pan and cook until wilted.
Stir in the Classico® Creamy Alfredo. Cook until heated through.
Pour the sauce with the mushrooms and spinach over the fettuccine and serve the with the chicken.