Preheat your oven to 350°F (175°C).
In a skillet over medium heat, melt 2 tablespoons of butter.
Add the chopped onions and sauté until they soften.
Incorporate the spinach and cook until wilted.
Transfer the spinach mixture to a bowl, adding ricotta, mozzarella, Italian seasoning, and salt and pepper. Mix well.
On a flat surface, lay out the lasagna sheets and place a small scoop of filling at one end of each. Roll them up tightly.
Arrange the roll-ups seam side down in a greased baking dish.
In a pot over medium heat, melt the remaining butter.
Combine pumpkin puree and heavy cream in the pot, stirring well.
Add nutmeg and season with salt and pepper. Simmer until thickened.
Mix in the parmesan cheese until fully blended.
Pour the sauce over the roll-ups.
Bake for 20 minutes.