Yes, absolutely! The parmesan cheese adds extra flavour and crisp to the topping, but if you don't have any the meal will still be really delicious. Alternatively, use a different kind of cheese. I often use a strong cheddar if I don't have parmesan. Crumbled feta, pecorino or another strong tasting hard cheese would also work. As always, there is nothing wrong with making the recipe your own!