Bring a large pot of salted water to a rolling boil over high heat. Add spaghetti and cook according to package directions until al dente. Reserve ½ cup pasta water, then drain spaghetti.

Rinse mushrooms under cold water and pat them dry. Slice into even pieces.

Heat olive oil in a skillet over medium heat. Add minced garlic and chili flakes, cooking until fragrant.

Add sliced mushrooms to the skillet, seasoning with salt and pepper. Cook until golden brown, about 7 minutes.

Combine drained spaghetti with sautéed mushrooms in the skillet. Add fresh parsley and Parmesan cheese, tossing to mix. Gradually add reserved pasta water to create a creamy sauce.

Serve immediately, garnished with additional Parmesan cheese and chili flakes if desired.