Bring a large pot of salted water to a rolling boil. Add spaghetti and cook until al dente, about 8-10 minutes. Reserve 1 cup of pasta water, then drain spaghetti.

Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add sliced button and oyster mushrooms, sauté for about 5 minutes until golden brown.

Lower heat to medium, add remaining olive oil and chopped garlic to the skillet, cook for 1-2 minutes until fragrant.

Sprinkle in chili flakes and add reserved pasta water. Season with salt and simmer for 2-3 minutes until sauce thickens.

Toss cooked spaghetti into the skillet with mushrooms and sauce, mix thoroughly. Add chopped parsley.

Transfer to serving plates, sprinkle with Parmesan if desired, and serve hot.