Layer the sliced potatoes and onion evenly in the bottom of the slow cooker.
Drizzle the melted butter and heavy cream over the potatoes. Sprinkle half the salt, half the pepper, and half the cheddar cheese on top.
Place the ham directly on the potato layer.
In a small bowl, stir together the cranberry sauce, orange juice, and orange zest. Pour this mixture over the ham so it coats the surface.
Sprinkle the remaining cheese, salt, and pepper over everything.
Cover and cook on low until the ham is heated through and the potatoes are fork-tender.
Let the dish rest for a few minutes before slicing the ham. Garnish with chopped parsley and serve the potatoes alongside.