Brush cauliflower with half of garlicky oil. Loosely cover with foil. Roast cauliflower until just tender, 35 to 40 minutes. Uncover and continue to roast until very tender, about 10 minutes more.
Garnish a bowl of chewy, nutty farro with roasted cauliflower florets, which turn sweet as they brown. The pair make a light vegetarian meal or a side for roast chicken or broiled fish.