Preheat the oven to 200 degrees Celsius.
Brush the lamb with olive oil and make incisions over its length with a small knife. Press slivers of garlic and rosemary leaves into the meat and place the lamb on a roasting tray in the oven for 20 minutes. Reduce the heat to 180C and cook for a further 70 minutes basting regularly in the juices. Add the pumpkin to the bottom of the pan 25 minutes before the meat is ready.
Rinse the quinoa thoroughly and place in a pan with 3 cups water. Bring to the boil, cover with a lid and reduce to simmer for 10 minutes. Remove the peas from the pods and add them to the pan, cover and cook for a further 5 minutes. Remove from the heat and set aside.
Heat the oil in a pan and sauté the onion and garlic until it's soft. Add the mushrooms and herbs and cook for a further 10 minutes or until the mushrooms are soft.
Stir the quinoa and peas through the mushrooms. Add the pomegranate seeds and serve with the pumpkin on top with slices of lamb.