Bring a large pot of salted water to a rolling boil, add spaghetti, and cook until al dente, about 8 minutes.

Before draining the spaghetti, scoop out half a cup of pasta water and set it aside.

Warm olive oil in a large skillet over medium heat until it shimmers lightly, about 1 minute.

Add thin garlic slices and red chili flakes to the oil, stirring gently until the edges turn golden brown, about 1–2 minutes.

Add the drained spaghetti and reserved water to the skillet, tossing for about 30 seconds until every strand glistens.

Sprinkle chopped parsley and lemon zest over the pasta, tossing briefly until vibrant and aromatic, about 30 seconds.