Place the spiral-sliced ham in a 6-quart or larger slow cooker, flat-side down. If the ham is too tall, cover the slow cooker tightly with a double layer of aluminum foil before adding the lid.
In a medium bowl, whisk together the brown sugar, reserved pineapple juice, honey, mustard, cloves, and cinnamon until smooth.
Rub about half of the brown sugar mixture over the ham, making sure to get some between the slices.
Arrange the pineapple slices over the top and sides of the ham, securing them with toothpicks if necessary.
Pour the remaining glaze over the top of the ham.
Cover and cook on the LOW setting for 3 to 4 hours, or until the ham is heated through (reaching an internal temperature of 140°F).
Every hour, spoon some of the juices from the bottom of the pot back over the ham to keep it moist.
Remove the ham carefully and place it on a serving platter.
Optional: Pour the remaining juices into a saucepan and simmer over medium-high heat for 10 minutes to create a thick syrup to pour over the sliced meat.
Garnish with fresh thyme and serve warm.