Preheat oven to 350 degrees F.
Cook pasta shells according to the package instructions, until al dente, and drain. Rinse with cold water and arrange on a baking sheet to cool until ready to stuff.
To make the filling, mix together pumpkin, pecorino cheese, egg white, nutmeg, cinnamon, sage, salt and pepper in a large bowl until all incorporated and set aside.
To make the marinara, drizzle olive oil in a large skillet and sauté garlic until fragrant. Add chicken broth, crushed tomatoes, pumpkin, pecorino cheese, sage, basil, nutmeg and salt mixing well until everything is combined. Bring to a boil then turn down heat to medium/low, cover and allow sauce to simmer for about 15 minutes. This is when you can stuff your shells.
Using a pastry bag (or a spoon), fill each shell with about 2 tablespoons of filling.
In a 9" x 13" baking dish, spread about 3/4ths of the marinara in the bottom of the dish and arrange shells on top. Cover with foil and bake for about 30 minutes.
Remove foil, sprinkle with additional pecorino cheese and bake uncovered for an additional 10 minutes until hot/bubbly and cheese is melted.
Top with remaining sauce, serve and enjoy!