Prepare BBQ sauce for basting:Mix mustard, coriander, cloves, garlic, pepper, oil, soy, vinegar, water and sugar together in a saucepan. Bring to the boil and simmer gently for 10 minutes.
Peel pineapple, reserving flesh for garnish. Place loin in a roasting tray, brush liberally with marinade and cover with pineapple skin.Roast meat in a moderate oven 180C/350F for about 2 hours, or until cooked, basting frequently with hot barbecue sauce.
Allow to rest for 15 minutes, servegarnished with diced fresh pineapple.