In a 12-inch skillet over medium, combine the oil and ginger, then cook, stirring often, until the ginger has softened and is just beginning to brown, 3 to 5 minutes. Add the chicken, onion, scallion whites and garlic; increase to medium-high and cook, stirring occasionally, until the chicken no longer is pink when cut into and the onion has softened, 7 to 9 minutes.
Add the fish sauce, oyster sauce, sugar, scallion greens and 1 tablespoon water; stir until the chicken and vegetables are evenly coated. Off heat, taste and season with salt then transfer to a serving dish.
