Preheat the oven to 220ºC, fan 200ºC, gas mark 7. Place the squash and onion on 2 separate baking trays.
Season and toss each with 1 tablespoon oil. Roast for 20 minutes, turning halfway through.
Meanwhile, mix together the breadcrumbs, rosemary and parmesan to make the topping. Put the pasta onto cook following pack instructions.
Place half the roasted veg in a food processor, along with the stock and nutmeg. Season and blend to make a sauce.
Preheat the grill to high.
Drain the pasta and toss through the squash sauce. Stir in the remaining roast veg, then tip into a 1.5-litre ovenproof dish and sprinkle on the breadcrumb mixture.
Grill until lightly golden. Serve immediately with a green salad.