Step 1 Preheat oven to 180°C. Line a large baking tray with baking paper. Place pumpkin on tray, spray with olive oil and roast for 25–30 minutes, or until golden; leave to cool slightly. Put pumpkin in a large bowl and mash roughly with a fork, leaving some texture.
Step 2 Meanwhile, spray a large non- stick frying pan with olive oil and set over medium–high heat. Sauté mushrooms for 4–5 minutes, or until golden. Add half the garlic and stir for 1 minute, then leave mushroom mixture to cool.
Step 3 Set a large non-stick saucepan over medium heat and spray with olive oil. Add onion and sauté for 5 minutes, or until soft. Add remaining garlic; cook, stirring, for 30 seconds, or until fragrant. Add tomato purée, reduce heat and simmer for 5 minutes. Season tomato sauce with cracked black pepper and set aside.
Step 4 Add cool mushrooms to mashed pumpkin with spinach and 1/2 cup of the ricotta; stir and season with nutmeg and pepper. Spread 1/4 cup of the tomato sauce across base of a 1.5-litre (6-cup capacity) baking dish. Lay lasagne sheets on a work surface. Spoon 1/3 cup of the pumpkin filling along centre of each sheet, roll to enclose filling and put cannelloni in dish; repeat with remaining lasagne sheets and filling.
Step 5 Spoon remaining tomato sauce over cannelloni to cover, dot with remaining ricotta and scatter with parmesan. Cover dish with foil; bake for 10 minutes. Remove foil; bake for another 10–15 minutes, or until golden and bubbling.