Bring a large pot of salted water to a boil. Add the jumbo pasta shells and cook according to package instructions, about 9-11 minutes, until al dente. Drain and toss with olive oil to prevent sticking.

Drain the tofu and place it in a food processor. Add nutritional yeast, garlic powder, onion powder, olive oil, and blend until creamy. Fold in canned pumpkin purée and freshly grated nutmeg.

In a medium saucepan, heat olive oil and sauté the chopped onion until soft, about 5 minutes. Add minced garlic and cook for 1 more minute. Gradually whisk in flour, then add the coconut milk, stirring until thickened, about 3-5 minutes.

Preheat the oven to 350°F (175°C). Spread a layer of garlic béchamel sauce in a baking dish. Stuff each shell with pumpkin filling and arrange them in the dish. Pour remaining béchamel sauce over the shells and garnish with sage.

Bake the stuffed shells for 22-25 minutes until the top is lightly golden and aromatic. Allow to cool slightly before serving.