Slightly adapted from Pillsbury.com
Melt butter over medium high heat in a 12-inch nonstick skillet. Add chicken breasts, and cook 3 to 5 minutes on the side, until golden brown.
Place chicken breasts into the bottom of a 3 1/2 - 4 quart slow cooker.
In a medium mixing bowl, whisk together the Alfredo sauce tomato pesto, Parmesan cheese, and Italian seasoning until well blended. Pour mixture over chicken breast to cover. Cover slow cooker and cook on the low heat setting 3 to 4 hours until chicken is no longer pink in center. Stir in spinach, and cook five minutes longer. Serve over pasta, rice, or potatoes.