You can either deep-fry the onion and squash until golden, then blot with kitchen paper, or rub them with oil and salt, spread over an oven tray and bake at 180C (160C fan)/350F/gas 4 for about 30 minutes, until soft and golden at the edges.
In another small pan, warm the gorgonzola, milk and sage very gently, so they form a soft sauce.
Meanwhile, keeping in mind that you want the pasta to be cooked at about the same time as the pumpkin, cook the fusilli in plenty of salted boiling water until al dente, then drain.
In a large bowl, toss the pasta first with the gorgonzola sauce, then add the squash mixture, toss again gently and serve immediately.