Place chicken breasts between two layers of plastic wrap and pound with a meat mallet or rolling pin to a uniform thickness. Discard plastic and transfer chicken to a clean work surface. Cut into bite-sized pieces and set aside.
Add chicken to hot skillet and cook until golden brown on each side, approximately 3-4 minutes per side. Season with salt and black pepper, to taste. Remove chicken from skillet and set aside.
Add half & half and chicken broth and scrape up any brown bits from the bottom of the pan with a spatula. Add oregano and grated cheese to skillet and whisk until cheese is completely melted, approximately 3-4 minutes.
Reduce heat to just below medium and add the sun-dried tomatoes and baby spinach. Simmer for 3-4 minutes, stirring occasionally, or until tomatoes are softened and the spinach wilts.
Add chicken and its juices back to skillet and simmer for another 3-5 minutes, or until chicken is heated through. Taste and adjust seasonings, as desired. Remove from heat and serve immediately with a side of Tuscan White Beans. Enjoy!