Sprinkle the aubergines with salt and leave to drain in a colander for 30 minutes. Wash well, drain and pat dry on kitchen paper.
Bring all the ingredients for the tomato sauce to the boil. Cover and simmer for 30 minutes. Remove the lid and cook for a further 20 minutes until the sauce is thick. Adjust the seasoning.
Meanwhile brush the slices of aubergine with the oil and place on 2 large baking sheets. Roast at the top of a preheated oven, 200°C (400°F), Gas Mark 6, for 10 minutes on each side until golden and tender.
Spoon a little tomato sauce into 6 lightly greased individual ovenproof dishes (or 1 lasagne dish) and top with a layer of aubergines and some Cheddar. Continue the layers, finishing with the Cheddar. Sprinkle the Parmesan over the top and bake at 200°C (400°F), Gas Mark 6, for 30 minutes until bubbling and golden.