Cut a pocket in the fat end of the chicken breasts. Be careful not to cut all the way through. Roll the ham (1 or 2 slices depending on how big they are) around the string cheese and slide it into the pocket. You may need a toothpick or two to close it up.
Bake at 350 or grill until the breasts are done (the cheese will start to ooze out), about 20-30 minutes depending on how thick the breasts are.
NOTE- When I grill these I like to use the bone-on skin-on breast to keep them nice and juicy. This will require a bit more cooking time.