Fill a large pot with water, add a generous amount of salt, and bring to a rolling boil. Add the pasta and cook until just al dente, about 8-10 minutes. Drain, reserving a cup of pasta water, and set aside.
While the pasta cooks, heat a deep skillet over medium-high heat. Add the olive oil and let it shimmer, then toss in the sliced mushrooms. Sauté for about 4-5 minutes, stirring occasionally, until the mushrooms turn golden brown and release their earthy juices.
Add the minced garlic to the skillet with mushrooms. Cook for about 1 minute until fragrant, stirring constantly to prevent burning. The garlic should turn golden and fill the kitchen with a nutty aroma.
Toss in the fresh spinach and cook for 2-3 minutes, stirring gently, until it wilts down and turns a vibrant green. If the pan gets dry, add small splashes of reserved pasta water or olive oil to keep everything moist and glossy.
Lower the heat to medium. Add the drained pasta to the skillet and toss everything together, allowing the flavors to meld. If needed, add a little reserved pasta water to loosen the mixture and create a glossy sauce that coats each strand of pasta.
Finish by squeezing over the lemon juice, then sprinkle with freshly grated Parmesan. Season with salt and pepper to taste, tossing again to distribute evenly. The dish should look glossy, with the greens and mushrooms well coated and the pasta glowing with flavor.
Remove from heat and serve immediately, garnished with extra Parmesan if desired. The pasta is tender, coated in a savory, earthy sauce, with bright green spinach and golden mushrooms making it visually appealing and delicious.
