Preheat oven to 220°C (425°F). Use the tip of a sharp knife to make 1/4-in. (5 mm) deep cuts every 1 in. (2.5 cm) or so, all over the fat layer on the lamb leg. This allows herbs and spices to penetrate into the meat.
In bowl, stir together the garlic, rosemary, oil, pepper and salt. Rub half the mixture over all sides of the lamb. Place on rack fitted into roasting pan. Add potatoes to leftover garlic mixture in bowl, turn to coat. Set potatoes around lamb. Pour rest of garlic mixture onto the lamb.
Roast lamb 15 min. at 220°C (425°F) then reduce heat to 190°C (375°F) and continue roasting 1 hr. Check internal temperature in thickest part of roast. Depending on preferred doneness, check for 54°C (130°F) for medium-rare, 60°C (140°F) for medium, 71°C (160°F) for medium-well. If greater doneness is desired, roast additional 15 to 20 min. between temperature checks. A 1.25 kg/2.5 lb roast will require approx. 1 hr. 20 min. to reach medium-rare. Tent lamb with foil 15 min. before slicing.
Meanwhile, make pesto by combining mint, parsley, cheese, pine nuts, zest, juice and salt in small food processor. Pulse to a coarse paste. Transfer to bowl, stir in olive oil. The pesto can also be made by hand by finely chopping herbs and mixing with the other ingredients. Makes 1/2 cup (125 mL). Lightly brush roast with pesto before slicing. Serve the remaining pesto as a condiment. Transfer roast and potatoes to platter. Garnish with herbs, fruits and veggies, as desired.