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

While the spaghetti cooks, heat 1 tablespoon of olive oil in a large skillet. Add halved button mushrooms and sauté for about 5-7 minutes until golden brown.

Reduce the heat to low and add remaining olive oil along with finely chopped garlic to the skillet. Cook for 1-2 minutes until fragrant.

Add reserved pasta water and chili flakes to the mixture. Season with salt and let simmer for about 2-3 minutes.

Add the drained spaghetti into the skillet and toss to combine, ensuring a well-coated dish. Add freshly chopped parsley.

Transfer to serving plates. Top with Parmesan and serve immediately while hot.