1. Combine first 8 ingredients in a small bowl.
2. Cut a horizontal slit through thickest portion of each chicken breast half to form a pocket. Stuff about 1/4 cup spinach mixture into each pocket. Carefully wrap each breast, in a single layer, with 2 slices prosciutto (chicken breast halves will be almost completely covered with prosciutto). Arrange chicken on a platter; freeze 15 minutes.
3. Preheat oven to 400°.
4. Heat a large ovenproof nonstick skillet over medium-high heat; coat pan with cooking spray. Add chicken and cook 3 minutes on each side or until browned.
5. Bake at 400° for 8 minutes or until chicken is done.
Note: Wrap prosciutto slices around chicken so that the ends of prosciutto tuck under the bottom side of the breast. It should be moist enough to adhere to the breast, but if not, secure with wooden picks.