Combine the Dijon, olive oil, salt and pepper and rub all over the meat, placing it on a rack over a baking dish, fat side up.
Combine all the crust ingredients in a food processor or mix well in a bowl and place on top of the meat, pushing it down firmly and covering all of the top of the meat.
Place in a pre-heated BBQ, with no heat directly under the baking dish and cook for approx 1 hour, check for done-ness and be prepared to cook for another 20 minutes. If the crust begins to burn, cover it with foil.
Rest, loosely covered with foil for 10-15 minutes then slice at the table and serve with potato and parmesan gratin and a green salad.