For the Béchamel sauce, heat the milk up in a separate saucepan, or in the microwave.
Meanwhile, heat olive oil in a large saucepan over medium-high heat.
Add the flour and stir with a whisk to combine.
Continue to stir as oil is all absorbed, and let the flour become toasted and nutty smelling, but not burnt, about 2-3 min.
Ensuring your milk is hot, and whisking continuously, start to add the milk in about 1/2 cup at a time. Stir until fully incorporated after each addition.
When you have added all of the milk, continue to whisk and ensure there are no lumps.
Add the sage, and season with salt and pepper to taste. Remember that the rest of the lasagna ingredients are really neutral in flavour, so this sauce is where the majority of the taste will come from. Season it up good!
Cook for another 2-3 min, and then reduce the heat to low, or set aside for later.
Pre-heat oven to 200°C /400°F. Scoop the seeds and stringy bits out of the pumpkin, and do what you will with it to get it peeled and sliced into uniformly sized bits. Remember, looks do not count here.
Place the pumpkin slices into a roasting pan and toss with olive oil to coat.
Place into hot oven, and roast until just barely tender. Remember the pumpkin will continue to cook in the lasagna, so it doesn't need to be very soft.
Deal with your noodles however you decided was best for you. If you're boiling them first, strain and set aside to cool so you can handle them.
When your pumpkin is cooked and slightly cooled and you're ready to start building your lasagna, get a nice big lasagna dish ready.
Spread some of your sauce on the bottom, followed by a layer of noodles.
Cover the noodles in a nice amount of sauce, a good 1/2 cup or so.
Layer down half of the pumpkin so that there is an even layer over the noodles, and sprinkle the pumpkin with 1/4 cup of Parmesan cheese.
Cover with noodles, and lay down all of the ricotta.
Sprinkle the ricotta with a little salt and pepper, and maybe a teensy sprinkle of crumbled sage as well.
Repeat with noodles, sauce, the other half of the pumpkin, another quarter cup of Parmesan, and finishing with a top layer of noodles and the remainder of the sauce.
If you think it's way too much sauce for the top, it's not. Just pour it all on, it'll thicken up as it cooks. Cover the sauce with the remaining 1/2 cup of Parmesan.
Bake covered for 30 min.
Uncover and bake for an additional 15 min, until top is brown and crispy.
Let stand for 10 min before serving.