In a large saucepan with a tight-fitting lid, heat the olive oil over medium heat. Add the pine nuts and swirl the pan until the nuts toast, about 2 to 3 minutes. Add the brown and wild rice and the farro and cook, stirring with a wooden spoon, until lightly toasted. Stir in 5 cups water, the lemon zest, thyme, and 2 teaspoons kosher salt. Bring to a boil. Reduce heat to a simmer, cover and cook undisturbed for 45 minutes. Check the texture of the rice, and if needed, continue simmering until tender and the liquid is absorbed, another 10 to 15 minutes.
Remove from the heat, scatter the scallions and lemon juice over the surface of the pilaf and set aside, covered, for 10 minutes. Fluff with a fork, stirring in the scallions, remove the herb sprigs and serve. Season with remaining salt and black pepper, to taste.