Don't be weirded out by the addition of fish sauce. It doesn't make the dish taste like fish, and it provides that spark of umami that makes it lip-smackingly delicious!
Remove the al dente pasta to the pan with the olive oil in it. Add lemon juice, fish sauce, pasta water and more butter, and toss to coat and emulsify. Add herbs and cheese at the end.
For ease and safety, rather than dumping a vat of boiling pasta into a colander, use a skimmer or tongs to remove your cooked pasta to the pan holding the sauce.
You'll know it's ready when the sauce is silky and coats the strands of pasta.
Use a Microplane to grate on some cheese and serve with more lemon zest and a sprinkle of finishing salt.