Wash the aubergines, cut them in half lengthways. Loosen the flesh from the sides of the skin and cut across the flesh several times. Sprinkle with salt and place cut side down in a colander on a plate. Leave to drain for 20-30 minutes to get rid of the bitter juices.
Heat the oven to 400F/200C/Gas Mark 6-7. Rinse and dry the aubergines, arrange them cut side up in a greased ovenproof dish, dot with half the butter, cover with a lid or cooking foil, and bake for 15-20 minutes until soft.
Meanwhile, peel and finely chop the onion and garlic, and wash and chop the tomato. Mince or finely chop the lamb. Heat the remaining butter with the olive oil in a pan over a moderate heat and fry the onion and garlic for 3-4 minutes until soft. Add the chopped tomato and cook for a further 2-3 minutes. Stir in the minced lamb, season to taste with the lemon juice, salt, pepper, and herbs, and heat gently until the mixture is hot.
Take the aubergines from the oven and allow to cool slightly. Then carefully scoop the cooked aubergine from the centres, leaving enough flesh to make a firm case. Dice the aubergine and stir it into the hot meat mixture. Adjust the seasoning. Pile the hot stuffing into the aubergine cases, sprinkle with the grated Parmesan cheese, and reheat in the hot oven for 5-10 minutes until golden and bubbling.