Boil salted water in a large pot. Cook jumbo pasta shells until al dente, about 10-12 minutes. Drain and toss with olive oil to prevent sticking.

In a blender or food processor, blend drained tofu, nutritional yeast, garlic powder, onion powder, salt, pepper, olive oil, lemon zest, and lemon juice until mostly smooth.

Add canned pumpkin, grated nutmeg, and vegan parmesan to the tofu mixture. Stir gently to combine and season to taste.

In a saucepan, heat olive oil over medium, sauté onion and garlic until translucent. Whisk in flour, then add coconut milk gradually until the sauce thickens.

Preheat oven to 350°F (175°C). Spread a layer of béchamel in a baking dish. Fill pasta shells with pumpkin filling and arrange in the dish. Pour remaining béchamel on top.

Cover with foil and bake for 22-25 minutes. Remove foil for the last 5 minutes to crisp tops.