Preheat oven to 375 degrees. In one large bowl mix together ingredients for pumpkin ricotta filling, and in another bowl mix together shredded mozzarella and parmesan cheeses. Set aside.
Heat oil in a pan (cast iron or non-stick works best) then add chopped onions and sausage. Brown all the way through until you no longer see any pink in the sausage. When the sausage and onions are nice and caramelized add chopped spinach. Stir to combine and then remove from heat.
Lightly oil sides of a casserole dish. I used a 9x9 square dish. Place a spoonful of pumpkin ricotta filling in bottom of dish as the very first layer. Add a layer of lasagna noodles. My lasagna noodles were a little wider so I used two and a half sheets (they did not break evenly but I formed an even layer with the pieces).
Next, spread about 1/4 of your pumpkin ricotta filling evenly over the noodles. Then add 1/4 of browned sausage and spinach mixture, and cover that with 1/4 of the mozzarella and parmesan cheese mixture. Cover with another layer of lasagna noodles then pumpkin ricotta layer, sausage and spinach, followed by a layer of cheese. The final layer will be the mozzarella and parmesan cheeses. Cover dish with foil.
Bake at 375 degrees for approximately 35 minutes. Remove from oven, remove foil, and bake for 10-12 minutes until cheese is golden brown. Garnish with extra parmesan and or chopped parsley. Cool for 15 minutes before cutting and serving. Serves 6.