Place ham into roasting pan. Combine cranberry sauce, 1/4 cup orange juice, brown sugar, and orange zest. Spread over ham, reserving at least one cup to serve alongside ham when finished.
Pour additional 1 1/2 cups orange juice into base of roasting pan and arrange orange slices and cranberries (optional) around ham. Place top on roasting pan or tent with aluminum foil and bake 1 hour.
Uncover ham and baste well with pan juices. Re-cover. Repeat every 15 minutes until the thickest part of the ham registers 140º on a meat thermometer.
Remove roasting pan from the oven and baste again. Let the ham stand for about 15 minutes before carving.