Cook the farro: Fill a medium pot half full of water and bring to a boil. Add the farro, reduce the heat, and simmer until the farro is tender, chewy, but still has an al dente bite - 10 to 20 minutes for pearled farro; 20 to 30 minutes for semi-pearled farro; up to 40 minutes for whole farro.

Drain, then spread onto a large plate or sheet pan to cool and dry for 20 minutes. This keeps it from continuing to steam which makes it mushy.

Make the lemon herb dressing: Whisk together the olive oil, lemon juice, thyme, garlic, mustard, salt, and several grinds of pepper in the bottom of a large mixing bowl. Add the farro and toss. Stir in the parsley and a pinch of red pepper flakes, if using. Season to taste and serve.