Bring a large pot of salted water to a boil, then add your pasta and cook until just al dente, about 8-10 minutes. Drain and set aside, reserving a cup of pasta water.
Zest the lemon using a microplane, then juice it. Mince the garlic and roughly chop the spinach. These prep steps will unlock vibrant flavors for the dish.
Heat the olive oil in a large skillet over medium heat until shimmering. Add the minced garlic and sauté for about 30 seconds until fragrant, the kitchen filling with a sweet, nutty aroma.
Add the chopped spinach to the skillet and cook until wilted and vibrant green, about 2 minutes. Stir occasionally and season lightly with salt and pepper.
In a blender, combine the soaked cashews, lemon zest and juice, a splash of reserved pasta water, nutritional yeast, and a pinch of salt. Blend until smooth and creamy, about 30 seconds. Taste and adjust lemon if needed for brightness.
Pour the creamy lemon sauce into the skillet with greens, stirring to combine and warm through for about 1-2 minutes. If the sauce is too thick, add a little more reserved pasta water to loosen it.
Add the cooked pasta to the skillet, tossing gently to coat each strand evenly with the lemon spinach sauce. Continue stirring for a minute until everything is well combined and heated through.
Serve immediately, garnished with extra lemon zest or nutritional yeast if desired, for an extra pop of flavor and color. Enjoy this bright, creamy, and tender green pasta while hot!