Well, with this dish, the aim is to have zucchini with crispy outsides and sumptuously soft insides.  The way we do that is to fry it over a high heat with the oil already hot before adding the slices to the pan.  That way the oil immediately sears the outside of the zucchini.  If the oil is not hot enough, the oil will penetrate the courgette slices and it will taste soggy and oily.  Pre-salting the zucchini slices can also help as it draws out some of the moisture from the inside of the courgette before cooking.  (see the notes above on pre-salting zucchini).