Preheat oven to 350 degrees F. Lightly coat a 9?13 baking dish with nonstick spray.

In a large pot of boiling salted water, cook pasta according to package instructions; drain well. Transfer to a baking sheet and drizzle with olive oil; set aside and let cool.

In a large bowl, combine ricotta, pumpkin, Parmesan, egg, sage, and nutmeg; season with salt and pepper, to taste. Stuff each shell with about 2 tablespoons of ricotta mixture.

To make the garlic parmesan cream sauce, melt butter in the skillet over medium heat. Add garlic, and cook, stirring frequently, until fragrant, about 1-2 minutes.

Whisk in flour until lightly browned, about 1 minute.

Gradually whisk in milk, and cook, whisking constantly, until incorporated, about 1-2 minutes.

Stir in half and half and Parmesan until slightly thickened, about 1-2 minutes. If the mixture is too thick, add more milk as needed; season with salt and pepper, to taste.

Spread ? cup cream sauce in the prepared baking dish. Arrange shells in dish, topping with remaining sauce.

Place into the oven and bake for 20-25 minutes, or until golden brown and bubbly.

Serve immediately.