Combine ricotta, garlic, milk, nutmeg and half the parmesan, then season well. Place lasagna sheets in a bowl, cover with boiling water and stand for five minutes or until softened. Grease a dish with one tablespoon oil. Lay one-third of the lasagna sheets over the base and arrange half of the pumpkin, prosciutto, chilli and sage in layers on top. Drizzle with a tablespoon oil followed by one-third of ricotta mixture. Repeat these layers once, finishing with a final layer of lasagna sheets and remaining ricotta. Cover the surface with a sheet of baking paper and foil, and bake for 40 minutes. Uncover, scatter with remaining parmesan and bake for 15 minutes until golden. Stand for five minutes before serving.