Drizzle olive oil over butternut squash cubes.
Place squash onto a baking sheet spreading the cubes out so they are not touching each other.
Roast butternut squash in an oven heated to 400 degrees F.
Roast squash for approximately 45 minutes or until tender, then let cool.
Meanwhile cook pasta shells according to package directions, let cool.
Mash butternut squash using a potato masher or fork.
In a medium bowl place butternut squash, ricotta cheese, mozzarella cheese, Parmesan, basil, salt, and pepper. Stir and combine well.
Place 1 ½ to 2 tablespoons of cheese mixture into each shell.
Place stuffed shells into a baking sheet that you have coated with ¼ cup of Alfredo sauce.
Spoon remaining sauce over tops of stuffed shells.
Preheat oven to 350 degrees F.
Place stuffed shells into oven and bake for 20-25 minutes or until cheese is melted.
Top with additional mozzarella cheese if desired.