Cook the pasta shells according to package instructions*. Drain and rinse shells and allow them to cool before handling.
*While the water is boiling for the pasta, combine the ground turkey, garlic, parsley, Italian seasoning, ¾ teaspoon of the salt, ¼ teaspoon of the black pepper, the minced onions, fennel seed, paprika, and crushed red pepper flakes in a mixing bowl. Mush together with a fork or your hands until thoroughly combined. While the pasta is cooking, mist a large skillet with cooking spray and bring over medium heat. Add the seasoned ground turkey to the heated pan and cook, breaking up the meat into bite-sized pieces and stirring occasionally until the meat is cooked. Add the spinach to the pan and stir. Cook for another 2 minutes or so until the spinach is wilted. Remove from heat and stir in the ricotta cheese until well combined.
Pour the broth and milk into a small saucepan and bring over medium heat. Cook until you start to see the first signs of bubbling and then add the pumpkin and reduce the heat to low. Whisk the pumpkin into the liquid until it absorbs and the sauce becomes creamy. Add the remaining ¼ teaspoon salt, ¼ teaspoon black pepper, marjoram, sage, and 1 ounce of the shredded parmesan. Stir together until the parmesan is melted into the sauce.
Pre-heat the oven to 350. Spread about ½ cup of the pumpkin sauce across the bottom of a 2 quart casserole dish (such as a 7x11) and set aside. Make sure the pasta shells are cool enough to handle, then use a spoon to stuff them full of the turkey/ricotta filling. Lay the stuffed shells in a single layer in the prepared casserole dish, open side facing up. Pour the remainder of the pumpkin sauce over the top of the stuffed shells to coat evenly. Sprinkle the remaining ounce of shredded Parmesan over the top. Place the dish in the preheated oven and bake for 30 minutes.