Preheat your oven to 375 degrees Fahrenheit.
On a large cutting board surface covered with parchment paper, butterfly the turkey breasts (see the video at the top of this post for a tutorial). Cover them with more parchment paper and pound them out to an even thickness using the smooth end of a meat tenderizer. Each turkey breast should be about one-inch thick.
Divide the stuffing mixture between the two turkey breasts and place mounds of the stuffing in a line along the middle of each of the breasts.
Roll them up carefully, bringing each end of the turkey breast into the middle over the stuffing.
Place each of the stuffed turkey breasts seam-side down and use butcher's twine to tie around each of the stuffed turkey breasts in 4 places and cut off the excess twine with a pair of kitchen shears.
Place the turkey breasts seam-side down on a greased rimmed baking sheet.
In a small bowl, combine the butter, garlic, salt and pepper, and parsley and spread it over the top and sides of each of the turkey breasts before adding them to the oven.
Roast the turkey breasts at 375 degrees Fahrenheit for about 25-35 minutes, or until the internal temperature of the turkey reaches 165 degrees Fahrenheit. The roasting times will be different for each oven and depending on the size of your turkey breast, so watch the turkey carefully after 20 minutes. For best results, and to ensure juicy turkey, use an instant-read meat thermometer inserted into the thickest part of the turkey breast instead of relying on roasting times.
When the turkey reaches an internal temperature of 165 degrees Fahrenheit, remove it from the oven and gently move the stuffed turkey breasts to a large cutting board surface. Cover them loosely with aluminum foil, letting them rest at room temperature for at least 15 minutes before slicing.