Place the ham, cut side down, into a roasting pan.
Cut the skin off the pineapple with a sharp knife and cut out any brown spots of skin left behind. Slice the pineapple into 1/2-inch slices and cut the cores out of the slices. Pin the slices onto the ham with toothpicks.
Bake ham in the preheated oven until a meat thermometer inserted into the thickest part of the ham reads 140 degrees F (60 degrees C), 1 1/2 to 2 hours.
While the ham is baking, mix the pineapple juice and brown sugar in a microwave-safe ceramic or glass bowl and microwave on medium power until the glaze is boiling and slightly thickened. Work carefully because the glaze will be sticky and very hot.
Pour about half the glaze evenly over the ham and pineapple about 1 hour before the end of baking; pour the rest over the ham about 30 minutes before the end of baking.
