Cook jumbo shells in salted boiling water for 8 minutes. Drain and rinse with cold water to stop the cooking process. (It's better to slightly undercook them than overcook them. They will continue to cook a little more when you bake them).
Make the pumpkin ricotta
Drain and press the tofu to get out as much liquid as possible.
Add tofu, pumpkin, puree, garlic, sage, nutritional yeast, olive oil, salt, and pepper to your food processor. Blend for about 1-2 minutes until smooth. (Add a splash of plain soy milk if needed to make it a ricotta texture.
Cook the sausage and kale
Saute your vegan sausage in 2 tbsp of oil until heated through, then add finely chopped kale and stir frequently until the kale is bright green and wilted. (This will take about 3-5 minutes for kale or about 1 minute for spinach.)
Add the tofu ricotta to the sausage and kale mixture and mix well.
Make the pumpkin alfredo
Pour 1/2 can of pumpkin puree, a can of coconut milk, 1/2 cup of water, 1 tbsp of starch, sage, salt, and nutmeg into a saucepan, and stir well.
Turn on the heat to medium and cook the sauce, stirring frequently, until it begins to boil. Then turn the heat down to low and let it simmer in the pan for 2 minutes stirring frequently.
Stuff and bake the shells
Preheat the oven to 350°F. It should be heated by the time you finish filling the shells. Pour half of the pumpkin alfredo in the bottom of the baking dish.
Fill the cooked jumbo shells with the tofu ricotta mixture (About 2 tbsp. in each shell) and place them into a large baking dish. (Hold the shell putting pressure on both ends so that it opens up to fill it).
Drizzle the remaining pumpkin sauce over the top of the stuffed shells.
Cover with foil and bake for 35 minutes at 350° F (176°C).
Take the foil off and bake the shells for an additional 10 minutes until bubbly in the center. (I bake them uncovered at the end to make them a little crispy on the edges. If you don't want that, you can bake them covered the whole time).
Notes
Slightly undercooking your shells will help to prevent them from breaking in the stuffing process.
If the shells start to stick together, rinse them again in cold water or place them in a pan of cold water before stuffing them.