In a bowl, mix mayo, spinach, feta cheese and garlic until blended. 

     Butterfly chicken breasts, making sure not to cut all the way through.  Spoon spinach mixture into chicken breasts.  Wrap each with 2 slices of bacon. 

     Place in shallow baking dish.  Bake, uncovered at 375 degrees for 1 hour, or until chicken is no longer pink and bacon is crisp.