Preheat the oven to 375°F. Add the mushrooms to a mixing bowl and drizzle with olive oil. Season with salt and pepper, then toss to coat. Spread onto a baking sheet in an even layer and roast for 20 minutes, until lightly crisp.

In a medium skillet over medium-high heat, add olive oil. When hot, add the onion and cook for 3–5 minutes, until softened. Add garlic and cook for 30 seconds more.

Transfer the sautéed onion and garlic to a high-speed blender. Add silken tofu, water, lemon juice, salt, and pepper. Blend on high for 2 minutes, until smooth and creamy.

Bring a large pot of salted water to a boil. Cook the fettuccine according to the package directions for al dente. Drain and return to the pot.

Pour the sauce over the cooked fettuccine and toss to coat evenly. Adjust seasoning to taste. Transfer to serving bowls, then top with the roasted mushrooms and chopped parsley. Serve warm.