Preheat oven to 425 degrees F (220 C). Line a large baking sheet with parchment paper or aluminum foil (greased with cooking spray).

In a small bowl, stir together the Panko breadcrumbs, melted butter, Italian seasoning, and 0.25 teaspoon salt until combined. Set aside.

In a large mixing bowl, toss together the diced butternut squash, 6 peeled garlic cloves, and 1 tablespoon olive oil until evenly coated. Spread the butternut squash out on the prepared baking sheet, and season generously with a few pinches of salt and pepper. Remove the garlic cloves and seal them in a small pouch made of aluminum foil, and set the pouch on the baking sheet next to the squash. Bake for 20 minutes, or until the butternut squash mashes easily with a fork and the garlic is soft and fragrant. Transfer the squash and garlic back to the large mixing bowl.

While the butternut squash is roasting, bring a large stockpot of generously-salted water to a boil over high heat. Add the jumbo pasta shells and cook al dente (or ideally cook until just a minute before they reach al dente) according to package instructions. Drain well.

Prepare the Alfredo sauce (see instructions below). Once sauce is made, add 1 cup of the Alfredo sauce to the large mixing bowl with the roasted squash and garlic, and mash together with a fork until smooth. Set aside the remaining Alfredo sauce.

In a 9x13-inch baking dish, spread out 0.5 cup of the remaining Alfredo sauce in an even layer. Stuff a tablespoon or two of the butternut filling inside each of the shells, and lay them in an even layer in the baking dish, filling-side-up. Spoon the remaining Alfredo sauce evenly on top. (Optional: if using the mozzarella, sprinkle it on top of the alfredo sauce.) Then sprinkle the Panko mixture evenly over the top of everything.

Bake uncovered for 15 minutes, or until the Panko mixture is crispy and starts to turn slightly golden. Remove from oven and serve immediately.

Heat 1 tablespoon olive oil in a large sauté pan over medium-high heat. Add 4 cloves minced garlic and sauté one minute, stirring occasionally, until fragrant. Sprinkle with 3 tablespoons all-purpose flour, and stir to combine. Sauté for an additional minute to cook the flour, stirring occasionally.

Slowly add 1 cup chicken or vegetable stock, whisking vigorously to combine until smooth. Whisk in 1 cup low-fat milk and 1 tablespoon chopped fresh sage, and bring the mixture to a simmer. Let cook for an additional minute until thickened, then stir in 0.75 cup freshly grated Parmesan cheese, 0.5 teaspoon salt, and 0.25 teaspoon black pepper until the cheese is melted and the sauce is smooth. Reduce heat to low and simmer until ready to use.

For efficient timing, it is recommended to start making the Alfredo sauce simultaneously with bringing the pasta water to a boil and cooking the pasta.