Prepare the pasta according to the package directions.
Bring a small saucepan filled with water to a boil. Add the cashews and allow to simmer for 10 minutes.
While the pasta water is coming to a boil and the cashews are simmering, add the diced onion and minced garlic to a large saute pan in a ¼ cup of vegetable stock or 2 tablespoons of olive oil over medium heat. Cook for about 3 minutes or until translucent.
Add the onions and garlic to the blender for the sauce.
Dice mushrooms, and add to the pan with the onions. Sauté until browned about 5 minutes. Add the spinach. Cover with a lid, to steam the spinach.
Drain the soaked cashews. Add them to the blender with the onions and garlic. Add the almond milk, vegetable stock, nutritional yeast, salt, black pepper, and lemon juice. Blend until smooth.
Transfer to a small pot. Heat on medium until the sauce is warm and thickens. Set aside.
Assemble the pasta: Add the drained pasta to the pan with the mushrooms and spinach. Pour the cashew cream sauce on top, and fold it all together until everything is well combined.
Serve topped with fresh parsley and a lemon wedge.