Place lamb on a chopping board lengthways, use a sharp knife to cut incisions right through the meatiest part almost to the bone, at 4cm thick intervals.
In a medium mixing bowl combine rosemary, thyme, garlic, capers, quince paste, breadcrumbs and two tablespoons of olive oil, mixing well. Season with salt and pepper.
Place spoonfuls of stuffing into the lamb incisions and tie with string to secure.
Scatter lamb with extra rosemary, drizzle with remaining olive oil, and season with salt and pepper. Cook in preheated oven for 2 hours, or until cooked to your liking*. Cover the top with foil after the first hour, to prevent stuffing burning.
For the salsa verde, combine all the ingredents together in a food processor, pulsing until finely chopped.