Prepare Your Casserole Dish: Begin by having a 9x13-inch oven-safe casserole dish ready to go.
Cook the Pasta Shells: Bring a large pot of water to a boil and cook the pasta shells for about 7 minutes until al dente.
Brown the Sausage: In a large skillet over medium-high heat, add the sausage and brown it while breaking it up into smaller pieces.
Make the Sauce: In that same skillet over medium-low heat, combine pumpkin puree, water, ricotta cheese, and nutmeg.
Combine Filling Ingredients: Set aside some sauce in another bowl before combining it with your sausage mixture.
Assemble Your Stuffed Shells: Carefully remove each pasta shell from ice water, stuff each shell with the sausage filling, and place them in your prepared casserole dish.