Combine rice, lemongrass, if using, ginger, salt, and 1¾ cups water in a medium saucepan. Bring to a boil, reduce heat to low, and cook, covered, until liquid is absorbed and rice is tender, 30–35 minutes. Remove from heat and discard ginger and lemongrass; fluff rice with a fork. Cover and set aside 5 minutes. Reserve ½ cup rice for Chicken, Mango, and Black Rice Salad. Serve rice topped with toasted coconut.