Preheat the oven to 200°C.
Place lamb on a roasting pan. With a sharp knife, make small incisions over the lamb and push some garlic and rosemary leaves each incision. Season the lamb with some cracked black pepper and a pinch of salt.
Roast in the oven for 20 minutes.
Reduce the temperature to 180°C and cook for a further hour and 10 minutes.
Mix together the cut vegetables in a large bowl and toss through the olive oil, seasoning and cumin. Arrange the veggies on a baking tray and place them in the oven in the last 15 minutes of the lamb cooking.
When you remove the lamb, toss the veggies to ensure they cook evenly and return them to the oven for a further 30 minutes.
Cover the lamb loosely in foil and to rest for 30 minutes while the veggies cook.
Once cooked, remove the veggies from the oven and toss through the parsley and lemon juice.
To MAKE THE MINT SAUCE
While the lamb is cooking, place the mint, sugar, water and vinegar in a blender. Season with a pinch of salt and process until well combined.
Slice the lamb and serve 150 g to each person with the mint sauce and spicy ratatouille.