Cook spaghetti in salted water according to package instructions until al dente. Reserve ½ cup pasta water, then drain.

Heat olive oil in a large skillet over medium-low heat.

Stir in red pepper flakes and cook for 10 seconds.

Add cooked spaghetti to the skillet and toss to coat in the oil.

Add a splash of reserved pasta water if needed for moisture.

Season with salt and black pepper.

Remove from heat and toss with parsley and Parmesan. Serve immediately.