First, cook the pasta according to the package instructions. Right before straining the pasta, remove ¼ cup of starchy pasta water and set it aside for later.
While the pasta is cooking, chop the vegetables and make the miso butter sauce. Melt the vegan butter, then add it to a bowl with the miso paste, nutritional yeast, plant-based milk, and lemon juice. Then, whisk together until the sauce is smooth and no clumps remain. Set aside for later.
Next, cook the mushrooms. Start by adding 2 Tbsp of oil to a pan and turning on the heat. Once the oil is hot, add in the mushrooms.
Cook the mushrooms for 10-15 minutes until all of the juices have been released, evaporated, and the mushrooms are getting crispy. Make sure to stir the mushrooms consistently while they cook.
Then, add in the minced garlic and salt and cook everything together for another 2-3 minutes.
Add in the spinach and stir it into the mushroom mixture so it starts to wilt. Then, pour in the miso butter sauce and mix it into the vegetables until they are coated.
Finally, add in the cooked pasta and reserved pasta water. Mix everything together until the noodles are coated in the sauce.
Serve topped with optional fresh oregano and enjoy!