Preheat the oven to 375°F (190°C) and lightly grease a baking dish with olive oil.
Cook the jumbo pasta shells according to package instructions until al dente. Drain and set aside to cool slightly.
In a large bowl combine pumpkin puree, ricotta cheese, egg, minced garlic, salt, black pepper, and nutmeg.
Add ½ cup mozzarella cheese and ¼ cup parmesan cheese to the mixture and stir until smooth and creamy.
Fill each cooked pasta shell with about 1–2 tablespoons of the pumpkin ricotta mixture.
Spread 1 cup of Alfredo sauce evenly across the bottom of the baking dish.
Arrange the stuffed shells in the dish in a single layer.
Pour the remaining Alfredo sauce over the shells.
Sprinkle the remaining mozzarella and parmesan cheese on top.
Bake uncovered for 25–30 minutes until the cheese is melted, bubbly, and lightly golden.
Let the dish rest for 5 minutes before serving.
Garnish with fresh parsley, fried sage, or extra parmesan if desired.