• Preheat your oven to 375F.

For The Sauce

• Heat the butter in a large skillet. Add the onions and garlic. Sauté over medium-high heat until soft, 3-5 min. 
• Add the mushrooms and cook until the mushrooms have darkened in color, 3-5 min.
• Add the chopped, fresh spinach and sauté for an additional 1-2 minutes, until the spinach has wilted. 
• Add the tomatoes (with their juices), tomato paste, water, bay, sage, rosemary, salt, and cinnamon. Simmer for 5 minutes, then remove the sauce from the heat and set aside. Remove the bay leaves before you use the sauce in your lasagna.

For The Cheese

• In a small bowl, mix together ricotta, egg, salt, and nutmeg. Set aside.

Putting It Together

• Prep your butternut squash ‘noodles’. Slice off the two ends of the squash and peel it with a sharp vegetable peeler. Once peeled, chop off the bottom bulb (containing the seeds). Place the neck of the squash upright on your cutting board and slice it into ¼ inch thick strips. (This can also be done using a mandolin slicer.) Set the strips aside.
• Grease an 8x8 baking dish and spread ⅓ of the sauce mixture into the bottom of the dish. Top with ½ of the butternut squash, and ½ of the ricotta cheese mixture. Continue layering with ⅓ of the sauce, the remaining squash, and the remaining ricotta cheese mixture. Finish it off with the last ⅓ of the sauce.
• Cover the dish with aluminum foil and bake for 30 minutes.
• After 30 minutes, the outside should be bubbly and the squash should be starting to soften. (You can check for this by inserting a knife through the center of the dish.) Remove the aluminum foil and continue baking the dish for 20 minutes.
• Remove the lasagna from the oven and top it with fresh grated Parmesan cheese. Return it to the oven (uncovered) for an additional 5 minutes, to melt the cheese.
• Remove the lasagna from the oven and let it stand (uncovered) for 10-15 minutes before serving.