Preheat the oven to 275 degrees . Place the ham facedown in a roasting pan. Cover tightly with foil and bake for 1 1/2 hours.
Meanwhile, in a medium saucepan, combine the brown sugar, maple syrup and mustard and bring to a boil over medium-high heat, stirring constantly. Cook until reduced slightly, about 2 minutes; set aside.
Brush the baked ham with the glaze, then top with the pineapple rings, securing them with toothpicks. Return the ham to the oven and bake uncovered until heated through, 25 to 30 minutes.