Bring a large pot of salted water to a boil. Cook the spaghetti according to package instructions until al dente, about 8–10 minutes. Reserve ½ cup of pasta water, then drain.

Rinse and slice mushrooms, setting aside. Ensure they are dry for proper sauté.

Heat olive oil in a large skillet over medium heat. Add minced garlic and chili flakes, sauté for about 1 minute until fragrant.

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

Add drained spaghetti to the skillet and pour in reserved pasta water. Toss everything until well combined.

Remove from heat and fold in parsley. Top with Parmesan cheese if desired.

Serve immediately, garnishing with extra parsley and chili flakes if desired.