Start by making the creamy spinach sauce. Heat a large, deep sauté pan over medium heat. Once hot, add 2 tablespoons of olive oil and swirl it around. Then, add the sliced zucchini and season with sea salt and ground black pepper. Sauté for about five minutes until the zucchini is very soft and slightly browned.
Next, add half of the minced garlic and 3 cups of baby spinach to the pan. Stir and sauté until the spinach has just wilted, which should take about one minute. Remove the pan from the heat once done.
Transfer all the sautéed zucchini, spinach, and garlic into a blender. To this, add the soaked pine nuts, cooked white beans, light miso, lemon juice, and vegetable stock. Season with additional salt and pepper if desired, keeping in mind that the miso is salty. Blend on high until smooth and creamy, which should take about one minute. Taste the sauce and adjust the seasoning as preferred.
While the sauce cools, cook your pasta by following the package instructions. Make sure to reserve 1 full cup of the pasta cooking water before draining.
Wipe out the sauté pan and return it to medium-high heat. Add the remaining 2 tablespoons of olive oil and swirl it around. Add all the sliced mushrooms in an even layer. Season with pepper and let them cook undisturbed for one full minute before stirring, then allow them to cook for another minute.
After the second minute, give the mushrooms a stir. They should start to glisten and release their juices. At this point, season them with salt and continue sautéing until deep golden brown and most of the liquid has evaporated, around four minutes. Add the remaining minced garlic and tamari to the pan and cook for another full minute.
Once the mushrooms are cooked, keep them warm in the pan. Reserve a few spoonfuls of the mushrooms to sprinkle on top later.
Add the drained pasta to the pan with the mushrooms, along with the creamy spinach sauce and any remaining baby spinach. Use tongs to stir it all together, adding enough of the reserved pasta cooking water to achieve a loose and creamy texture. Season to taste with additional salt and pepper.
Once the sauce is to your liking and the spinach has wilted, top the pasta with the reserved mushrooms and a sprinkle of chili flakes if you’re feeling adventurous. Enjoy your meal immediately!