Cook your pasta in a pot of boiling, salted water to al dente according to package directions.
While the pasta is cooking, place a large saute pan over medium heat. Swirl the oil in the pan and add the red pepper flakes and onions, cooking until the onions are tender, about 3 minutes. Add the garlic, and cook another 1 minute until fragrant. Add the mushrooms to the pan and saute them until they are tender and begin to brown, 5 more minutes. Stir in the fresh herbs and spinach so that they just being to wilt and turn the heat down to low. Season generously with salt and pepper to taste.
Drain the pasta. Stir the yogurt and lemon juice into the pasta until coated and creamy. Toss the pasta with the mushroom and spinach mixture. Serve with freshly grated parmesan as desired.