Preheat oven to 400 degrees.
Toss butternut squash with 2 tablespoon of the walnut or olive oil, and salt and pepper. Place on a baking sheet and roast till cooked through, about 20-25 minutes. Remove from oven and lower oven to 350 degrees.
Meanwhile bring a large pot of salter water to a boil. When water boils, add in shells and cook till al dente. Drain and rinse with cool water and set aside.
Saute sausage in a large skillet until cooked through, and add in the kale, cooking till just wilted.
Once the butternut squash is done roasting, add to a blender or food processor, along with the half and half, water and 2 tbps of walnut or olive oil and a generous pinch of salt and pepper. Blend on high until smooth. Add in butternut squash to saute pan with sausage and kale, and stir till combined.
In a medium bowl, combine the ricotta cheese, goat cheese and half of the mozzarella and Parmesan cheese, along with a generous pinch of salt and pepper. Stir till combined.
To assemble the dish, start by spooning half the butternut squash and sausage mix into the bottom of the baking dish. Stuff each shell with about 1-1.5 tablespoon of the ricotta cheese mixture, and lay down in the pan. Proceed till filling is gone and pan is filled with the shells, tightly packed together. Top with the remaining sauce. If using a smaller pan, you can also layer the shells starting with ½ of the sauce, shells, ¼ sauce, shells and topping with remaining ¼ sauce.
Top with remaining mozzarella and Parmesan cheese, and bake until cheese is melted, about 20-25 minutes.