Preheat the oven to 375°F (190°C / Gas Mark 5).
In a medium saucepan, combine the pineapple juice, brown sugar, honey, mustard, cinnamon sticks, cloves, and nutmeg. Bring to a simmer, then reduce the heat and cook for 15-20 minutes until thickened.
Place the pork tenderloin in a baking dish. Make slices along the top, about ¾ inch apart, without cutting all the way through.
Brush half of the glaze over the pork, making sure it gets into the slices.
Cut the pineapple slices in half and tuck into the cuts on the pork.
Bake for 25–30 minutes, or until the pork reaches 145°F (63°C) internally. Remove from the oven and increase the heat to 400°F (200°C / Gas Mark 6).
Brush on the remaining glaze and return to the oven for 10 minutes, or until the pineapple and glaze are slightly caramelized.
Let the pork rest for 10 minutes before slicing. Serve with your choice of sides and enjoy!