Mix the five spice powder, salt, pepper and oil then rub the pork with this mixture. Set aside (you can marinate it for up to 2 hours)
Preheat the oven to 180°C.
In a large frying pan heat the oil and sear the pork all over.
Meanwhile, prepare the other ingredients - slice the onion, halve the plums, mince the ginger & garlic, then mix the hoisin sauce with the sesame oil, soy sauce, water, rice vinegar & half of the honey.
Put the tenderloin into a roasting dish, scatter the plum, star anise and the onion pieces around it, then brush the pork with the hoisin glaze. Pour most of the remaining mixture over the plums. Add a drop of water too.
Cover the dish with foil, then roast in the oven for 20 minutes.
Meanwhile, add the other half of the honey to the remaining hoisin glaze.
Take the dish out of the oven, remove the cover and brush the glaze over the pork. Scatter the sesame seeds on top.
Put the dish back in the oven and roast for 5 minutes, until the meat is golden and the sticky glaze has caramelised.
Rest the pork for 5 minutes, then slice it.
Serve with the plum sauce and the sliced spring onions scattered on top.