One minute before pasta is finished cooking, heat up a pan. Add 4 tbsp olive oil, lemon zest, grated garlic and chili flakes. Cook 20 seconds on low heat until garlic sizzles, don’t let it turn color. Add lemon juice, 1/4 tsp salt. Take pasta directly from cooking pot and add to pan. Stir well and add more salt if necessary. Add chopped parsley and grated parmesan, if using. If pasta is too dry, add some of the pasta cooking liquid. Serve hot.