Preheat the oven to 180°C conventional oven/ 160°C fan-forced (350° Fahrenheit/Gas 4). Grease a baking dish with butter or margarine.
Line a separate large baking tray with baking paper. Place the pumpkin on the prepared baking tray. Add sage, red onion and garlic. Drizzle olive oil over the pumpkin and sage mixture, then pour over vegetable stock. Toss to coat evenly. Bake for 40 minutes or until tender and golden. Once cooked, discard garlic clove.
Meanwhile, to make the Besciamella sauce, melt the butter in a medium-sized saucepan over medium heat until foaming. Add the flour and stir with a wooden spoon to form a smooth paste (a roux). Allow the flour and butter mixture to cook for a minute (but do not allow it to brown). Remove from the heat. Slowly pour the cold milk into the roux, stirring constantly, until the mixture is smooth. Add the bay leaf and return to medium heat. Cook, stirring with the wooden spoon until the Besciamella comes to the boil and thickens (approximately 10 minutes). Remove from heat. Season with salt to taste and stir in freshly grated nutmeg. Set aside to cool slightly.
Heat the olive oil in a medium-sized frying pan over medium heat. Add the zucchini (courgettes) and cook for 2 minutes on each side or until tender and lightly golden. Repeat cooking of remaining zucchini. Set aside to cool slightly. Meanwhile, use a potato masher or the back of a spoon to press the pumpkin and sage mixture to lightly mash.
Remove the fresh lasagne sheets from the packet.
Note: If you are making your own pasta for this recipe, use 1 quantity of fresh egg pasta
Ladle a bit under 1/3 of the Besciamella (Bechamel) sauce to just cover the base of the prepared baking dish. Cover the Besciamella with a layer of pasta sheets that overlap slightly. Spoon Besciamella sauce where the pasta overlaps. Ladle 1/2 of the pumpkin and sage sauce over the pasta sheets. Arrange a layer of the zucchini over the pumpkin and sage sauce. Cover with a layer of pasta sheets, overlapping slightly. Ladle half of the remaining Besciamella sauce to cover the pasta (including where the pasta overlaps). Sprinkle 1/2 of the mozzarella cheese evenly over the Besciamella, followed by an even layer of the baby spinach. Arrange a layer of pasta sheets, overlapping slightly. Ladle the remaining pumpkin and sage sauce in an even layer over the pasta sheets, followed by an even layer of the remaining Besciamella. Sprinkle the remaining mozzarella cheese. Finish with an even layer of Parmigiano Reggiano sprinkled to cover the lasagne and few knobs of butter (or margarine) on top.
Bake for 40 minutes, then remove from the oven. To confirm that the lasagne is cooked, insert a knife in the centre of the baking dish and hold it there for a few seconds – if the knife blade is hot, the lasagne is ready. Leave to rest for a minimum of 10 minutes before serving.
Cut the Vegetable lasagne into 6 portions and serve immediately – buon appetito.