1.Preheat oven to 200°C/400°F.
2.Make harissa. Place capsicum on oven tray; roast about 20 minutes or until skin blisters and blackens (leave the oven on). Cover capsicum with plastic wrap, stand for 5 minutes; peel away skin, discard stems and seeds. Meanwhile, heat oil in small frying pan; cook onion and garlic, stirring, until softened. Add spices; cook, stirring, until fragrant. Process capsicum and onion mixture with remaining ingredients until smooth.
3.Combine couscous with the water in medium bowl; stand 5 minutes. Stir harissa into couscous.
4.Place lamb, fat-side down, on board. Spread couscous mixture over lamb; top with pine nuts and mint. Roll tightly to enclose filling; secure with kitchen string at 2cm (¾-inch) intervals.
5.Heat oil in large baking dish; add lamb, cook until browned all over.
6.Transfer dish to oven; roast, uncovered, about 45 minutes. Cover lamb with foil; stand 10 minutes before serving.
You could use 2 tablespoons finely chopped fresh mint instead of dried mint when making the harissa.Note