Preheat oven to 325 degrees F. Add the brown sugar, whole grain mustard, maple syrup & orange zest to a small bowl. Mix to combine; the glaze will have the consistency of a thick paste. Set aside.
Add the fresh squeezed orange juice to the bottom of an 8×12 baking dish, sprinkling in a couple of whole cloves. Set aside. Using a paring knife, score the ham with a set of lines, approximately 1-inch apart & approximately 1/4-inch deep. Rotate the ham 45 degrees, and score the ham with a second set of lines, approximately 1-inch apart & approximately 1/4-inch deep, creating a cross-hatch or diamond pattern of scorelines across the entire ham.
Spoon half of the prepared glaze on the ham, using your hands to rub it over the entire surface of the ham.
Arrange the thinly sliced orange over the entire surface of the ham, using whole cloves to tack the oranges in place. Spoon the remaining maple glaze over the ham & orange slices, again using your hands to rub it over the entire surface of the ham. Transfer the ham to the prepared baking dish, covering with aluminum foil.
Bake the ham until a thermometer inserted into the center of the ham registers 145 degrees F, about 15 minutes per pound. Halfway through the total bake time, remove the foil from the baking dish & use a baster to baste the liquid that accumulates at the bottom of the baking dish back over the surface of the ham. Return the ham to the oven (uncovered), basting every 15 minutes of the remaining baking time. With 30 minutes left in the total baking time, increase the heat to 375 degrees F to help the oranges caramelize.
Remove the ham from the oven & carefully transfer to a cutting board. Set aside to rest for 15 minutes before carving the ham into 1/4-1/2-inch thick slices as desired.