Make the caramelized onions. Heat a large skillet over medium-low heat and add the butter. Add in the onions with a pinch of salt and pepper and stir. Cook, stirring often, until the onions caramelize, about 30 to 40 minutes. Once the onions are golden and caramelly, transfer them to a plate.
Saute the spinach. Add a drizzle of olive oil to the same skillet and toss in the spinach and garlic. Stir, cooking until the spinach wilts. Transfer the mixture to a separate plate from the onions.
Prepare the noodles. Meanwhile, boil a pot of salted water and cook the lasagna noodles until they are al dente. Once they are finished, lay them out on a clean towel or parchment paper. Don’t let them stick together!
Preheat your oven to 350ºF
Make the pumpkin ricotta. In a large bowl, whisk together the ricotta, pumpkin, parmesan, egg, salt and pepper Stir until combined.
Assemble the roll-ups. Top with 3 tablespoon of the pumpkin ricotta per noodle and spread out the mixture evenly. ( I like to place the 3 tablespoons on all the noodles before spreading it out, this way, if you need more mixture, you can add the leftovers.) Then sprinkle the mozzarella cheese and spinach on each noodle. Then go through and top each with the caramelized onions. Roll up each lasagna noodle tightly from the end.
Make Bechamel. Heat the butter in a large skillet over medium heat. Once sizzling, whisk in the flour and let it cook for 2 to 3 minutes, until fragrant and golden. Slowly whisk in the milk, stirring the entire time to avoid lumps. Whisk constantly until the mixture thickens, about 3 to 4 minutes.
Once thicken, reduce the heat to low and stir in the Boursin cheese. Taste the sauce and if needed, add more salt and pepper.
Assemble the pumpkin lasagna roll-ups. Ladle ½ the sauce into the bottom of a 9x13 inch baking dish. Place the lasagna roll-ups seam-side down in the dish. Pour the remaining sauce over top of the rollups. Sprinkle the remaining mozzarella on top, along with a sprinkle of parmesan cheese. Bake for 25 to 30 minutes, until golden and bubbly.