Let the pork stand out while you chop the sweet potatoes to prepare for cooking. Place the cubed sweet potatoes covering the bottom of a roasting pan to create a rack/bed for the pork loin to sit on.
Using a sharp knife, score the fat that covers the top of the pork into square shapes. Place the pork, fat side up, on top of the sweet potatoes.
In a glass bowl; mash the chopped garlic with a fork then add the 1/2 tsp salt, 1/2 tsp pepper, 1/8 tsp nutmeg, and 2 tsp olive oil. Continue mashing into a sort of paste. Stir well to combine and then rub the garlic mixture into the fat on the pork and get into the scores real well.
In another bowl; mix the honey with the orange zest and juice, Grand Marnier, 1/8 tsp salt, 1/8 tsp pepper, 1/8 tsp nutmeg, and 2 TBSP olive oil.
Stir until all is dissolved then pour all around the pork over the sweet potatoes.
Slice the other orange and place slices all around the pork on the sweet potatoes.
Place in the oven, uncovered, and roast for 1 1/2 hours.
Turn the pan and stir the sweet potatoes a little bit about midway thru cooking.
Roast until the internal temperature reaches 150-155 degrees F when a meat thermometer is inserted. (Never cut meat to check doneness because it dries it out-get a meat thermometer they are worth it!).
Cover the meat with foil and let it rest for 15-20 minutes before cutting to serve. (Meat that is sliced immediately dries out, you want the juices to redistribute. Also, the meat's temperature will rise at least 5 more degrees while resting and then it will be a perfect 160 degrees F!).
Serve on a platter surrounded by the sweet potatoes and orange slices!