Following package instructions, place the frozen spinach in a dish and microwave until thawed. Drain the spinach and squeeze out as much excess liquid as possible. Place the spinach in a bowl and allow it to cool.
Mix together the cooled spinach with cream cheese, shredded cheese, and mayonnaise. Set the mixture aside until ready to use.
Heat a skillet over medium heat.
Place the chicken on a paper towel and pat dry—Season, the chicken with salt, pepper, and Italian seasoning.
Add the olive oil to the heated skillet and carefully add the chicken breasts. Cook until lightly brown and the chicken releases easily from the pan, about 2-3 minutes.
Once the chicken has been turned over, cook the chicken for about one more minute and top with the creamy spinach. Cover the pan and cook for 2-3 more minutes. The chicken is done when it reaches 165 degrees F.