Bring a large pot of salted water to a boil. Add the spaghetti and cook until al dente, about 8-10 minutes. Reserve ½ cup of pasta water before draining.

While the pasta cooks, rinse, dry, and slice the mushrooms into uniform thickness.

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

Add sliced mushrooms to the skillet, season with salt and pepper, and sauté for about 7 minutes until browned.

Toss the cooked spaghetti into the skillet and gradually add reserved pasta water while mixing until well coated. Stir in chopped parsley and Parmesan cheese.

Remove from heat, adjust seasoning if necessary, and serve immediately topped with additional Parmesan and chili flakes as desired.