Place the cashews in a heatproof bowl and cover them with boiling water. Let them soak for 10 minutes, then drain well. For an even smoother sauce, soak the cashews in cool water for 4 hours or overnight.
Bring a large pot of generously salted water to a boil. Cook the spaghetti according to the package directions until al dente. Before draining, reserve about 1 cup of the pasta water.
While the pasta cooks, prepare the sauce. Add the soaked cashews, plant-based milk, nutritional yeast, lemon juice, Dijon mustard, garlic powder, onion powder, black pepper, and salt to a high-speed blender.
Blend on high until completely smooth and creamy. Scrape down the sides as needed and blend again until the sauce has a silky consistency.
Heat the olive oil in a large skillet over medium heat. Add the chopped vegan bacon and cook for 3–4 minutes, stirring occasionally, until lightly crisp.
Add the minced garlic, smoked paprika, and black pepper. Cook for about 30 seconds, stirring constantly, until fragrant.
Reduce the heat to low and add the drained spaghetti to the skillet. Pour the creamy cashew sauce over the pasta and toss continuously with tongs until the noodles are evenly coated.
Add reserved pasta water a little at a time, tossing between additions, until the sauce becomes smooth and glossy and clings to the spaghetti.
Warm the pasta gently for another 1–2 minutes, but avoid letting the sauce boil. Taste and adjust the seasoning with additional salt, pepper, or nutritional yeast as desired.
Divide the Vegan Carbonara between bowls and finish with fresh parsley, vegan Parmesan or nutritional yeast, and plenty of freshly cracked black pepper.