Heat the oil in a large pan and fry the onion until soft, then add the garlic and minced lamb and thoroughly brown. Add the tomato puree, chopped tomatoes, water, stock cube, cinnamon and basil.
Bring to the boil, then reduce to the lowest setting and simmer for 10 minutes.
Add the sweet corn and simmer for a further 5 minutes.
Meanwhile cook the sweet potato in boiling water. When the lamb mixture is cooked spoon it into a serving dish, top with the sweet potato pieces and sprinkle with the Parmesan and mozzarella.
Place under a hot grill for a few minutes until golden brown and bubbling.