Add the water, farro, and cauliflower to a large pasta pot off the heat. Let the farro soak while you prepare the onions and garlic. Peel the onions, cut them in half, then slice them up and add them to the pot. Peel your garlic, cut off the root ends, and slice the garlic thinly. Add the garlic to the pot.
Stir in the tomato paste, olive oil, salt and red pepper flakes. Cover the pot and put the heat on high until the water comes to a boil. When it is boiling, remove the cover, lower the heat until the pot is simmering gently, and set a timer for 35 minutes.
Stir the pot occasionally to prevent sticking. After 35 minutes, the farro should be al dente and most of the liquid will have absorbed. Do not drain any excess liquid.
Serve the farro and cauliflower with extra olive oil to drizzle on top and Parmesan on the side, if desired. Garnish with basil or parsley (optional). Store leftovers in the refrigerator for up to 5 days.
There are three kinds of farro: whole grain, semi-perlato, and pearled, with the highest nutritional value being in the whole version, and the least amount in the pearled, although that's still a good option. I have not been able to find whole-grain farro at the store, but if you find it, it will likely take at least an hour to cook and may require overnight soaking. Follow the directions on your package.