Heat the butter in a medium saucepan over medium heat. Add the scallions and saute for 2 to 3 minutes. Add the rice and stir until the rice is fully coated with butter.
Add 3 cups water and bring to a boil. Add the salt and pepper, cover and reduce the heat to a simmer. Cook until the liquid is absorbed and the rice is al dente, 18 to 20 minutes.
Remove from the heat; fluff the rice with a fork; and stir in the parsley and the lemon zest, if using.