Heat oven or Big Green Egg to 350º
Melt butter in a large skillet on medium heat.
Once melted, add apples and cook for 2 minutes, stirring frequently.
Add water and stuffing mix; cover. Let stand 5 minutes, then mix lightly.
Spoon stuffing mixture onto cut side of meat to within 1/2" of the edge; or, place stuffing between two loins. Roll up and tie together with butcher's twine. Secure, seam side down, in a shallow roasting pan, which has been sprayed with non-stick cooking spray.
Bake for one hour.
Mix syrup, mustard and rosemary in a small bowl.
Spread over meat. Bake an additional 20-30 minutes, or until internal temperature of meat is 160ºF.
Remove roast from roasting pan. Gently tent with foil and allow to rest for 5-10 minutes.
Slice and serve.