Pancetta-wrapped Turkey Breast Stuffed with Spinach and Feta

Preheat oven to 350 degree F. Cut each turkey breast half almost in half horizontally, leaving 1 inch uncut. Open like a book and lay flat between 2 pieces of plastic wrap. Using a meat mallet, pound each breast half to 1/2-inch thickness (about a 10x12-inch rectangle). Remove top piece of plastic w