Aubergine is much healthier if you bake it instead of frying. Aubergine tends to absorb lots of oil whilst cooking. If you happen to have fresh basil, sprinkle it on the aubergine when layering instead of adding it to the sauce.
You can substitute tomato paste for tomato sauce. To do so, dissolve 100g paste in 1 ½ cup of water, add salt to taste and a spoonful of sugar.