"An non-gluggly, healthy lasagna recipe where vegetables rule! You could also make this a full vegetarian version by omitting the ground beef and substituting TVP or finely diced mixed vegetables (zucchini, carrot, celery, onion)."
Fill a saucepan with 1/2 inch of water, then add pumpkin pieces. Bring to a boil over high heat, then reduce heat to medium-low, cover, and steam until the pumpkin is very tender, 10 to 15 minutes. Drain pumpkin, then mash with 1 tablespoon butter, cinnamon; salt and pepper to taste, then set aside.
Melt 2 tablespoons butter in a saucepan over medium heat. Whisk in flour and cook, stirring constantly, until the paste just begins to turn golden, about 2 minutes. Whisk in milk gradually so that no lumps form. Bring to a gentle boil. Add the bay leaves, and reduce heat to low or warm. Allow to gently cook for 10 to 15 minutes, stirring frequently, then remove from heat.
Heat 1 tablespoon olive oil in a large skillet over medium heat. Stir in onion, fennel, and garlic; cook until the onion has softened and turned translucent, about 5 minutes. Add spinach and cook until wilted. Scrape mixture into a large bowl, and mix well with ricotta cheese and nutmeg.
Using the same skillet, heat another 1 tablespoon olive oil over high heat. Brown ground beef in oil, mixing thoroughly to break into small pieces. Once browned, reduce heat to medium-low and pour off excess grease. Stir in tomato paste and tomato puree. Gently simmer until thickened, about 10 minutes.
Preheat oven to 400 degrees F (200 degrees C). Grease a 9x13 inch lasagna dish.
Line the bottom of the lasagna dish with 4 noodles, do not overlap. Spread the ricotta mixture evenly over noodles, then sprinkle with 1/3 of the Parmesan cheese. Place another 4 noodles on top of the ricotta, then spread with evenly with the mashed pumpkin. Place the remaining 4 noodles on top of the pumpkin and top with the tomato sauce; sprinkle with another 1/3 of the Parmesan cheese. Stir the white sauce until smooth, then discard the bay leaves; pour the sauce over top of the lasagna. Sprinkle with remaining Parmesan cheese.
Place lasagna dish onto a foil-lined baking sheet (to catch any spills). Bake in preheated oven until the noodles have softened, and the white sauce has turned bubbly and golden brown, about 30 minutes.