Bring a large pot of salted water to a rolling boil and cook the pasta until just al dente, about 8 minutes. Drain, reserving a cup of pasta water, and set aside.
While the pasta cooks, heat a large skillet over medium heat. Add a tablespoon of olive oil, then sauté the sliced mushrooms for about 5-7 minutes, until they are deeply browned and fragrant, stirring occasionally.
Add the minced garlic to the skillet with the mushrooms and cook for 30 seconds until fragrant, watching closely so it doesn’t burn.
Toss the fresh spinach into the skillet and stir quickly to wilt, about 2-3 minutes. If the skillet gets dry, splash in a little reserved pasta water to loosen everything up and help wilt the greens evenly.
Reduce the heat to low, then add the drained pasta to the skillet with the vegetables. Pour in about 2-3 tablespoons of the reserved pasta water and squeeze in the lemon juice. Toss everything together gently, allowing the flavors to meld for 2 minutes.
Stir in the freshly grated Parmesan cheese and season with salt and pepper to taste. If the mixture seems dry, add a splash more of the reserved pasta water to create a silky, cohesive sauce.
Remove the skillet from heat and let sit for a minute to allow the flavors to settle. Serve immediately, garnished with extra Parmesan if desired, and enjoy the vibrant aroma and creamy texture.
