Heat 1 tablespoon of the oil in a large flameproof casserole. Add the lamb and fry gently for 5 minutes. Remove the lamb and set aside.
Heat the remaining oil in the casserole, add the onion and aubergine and fry for about 5 minutes until beginning to colour. Add the garlic, tomatoes, tomato paste, sugar and stock and bring to the boil. Reduce the heat, cover the pan and simmer gently for 5 minutes.
Return the lamb to the casserole and stir into the vegetables. Cook gently for 15 minutes. Check the seasoning.
Put the spring onions, Parmesan, wine vinegar or lemon juice and the olive oil into a blender or food processor and whizz to a coarse paste. Transfer this pesto to a small bowl.
Spoon the stew into bowls and top with spoonfuls of pesto. Serve with crusty bread.