Preheat oven to 350°F.
Cook the pasta shells in well salted water according to package directions until just al dente. Drain. Transfer to a large plate or baking sheet in one even layer to cool.
Meanwhile, heat the oil in a non-stick skillet over medium heat. Add the onion and sauté until soft and translucent, about 4 to 5 minutes. Add the garlic, basil, salt and pepper and sauté until fragrant, about 1 to 2 minutes. Add the tomatoes, stir well, and simmer for 10 to 15 minutes.
While the sauce is simmering, crumble the tofu into a mixing bowl. Add the pumpkin, sage and chopped kale. Mix thoroughly. Set aside.
Pour about 1 cup of sauce into the bottom of a 9x13 pan and spread evenly. Using a spoon, stuff each pasta shell with about 2 tablespoons of the tofu mixture and place them in a single layer in the dish. Pour the rest of the sauce over the top of the shells.
Bake for 20 to 30 minutes until heated through.