Rinse the quinoa in a fine-mesh strainer with cool running water before cooking to remove the saponin, a natural coating on the quinoa which can be an irritant to the stomach if not removed. Some quinoa is sold pre-rinsed.
In a saucepan bring the quinoa and broth to a boil. Add the currants, cover and reduce heat to low. Cook for 15 minutes. Turn off the heat, leave covered, and let sit for 5 minutes. After 5 minutes open the pan and lightly fluff the quinoa with a fork to separate the grains. Gently stir in the walnuts and scallion. Serve warm or at room temperature.