Rinse rice in several changes of cold water in a large bowl until water runs clear. Drain in a colander.
Transfer rice to a 4-quart heavy saucepan, then add water (3 1/3 cups) and bring to a boil. Reduce heat to low and cook, covered, until steam holes appear on surface and water is absorbed, about 13 minutes. Remove from heat and let stand, tightly covered and undisturbed, 5 minutes. Fluff rice with a fork and spread in a large shallow baking pan to cool quickly, about 45 minutes. Chill, covered with plastic wrap, at least 4 hours.
Heat a wok or 12-inch heavy skillet over moderate heat until a drop of water vaporizes instantly. Pour oil around side of wok, then tilt wok to swirl oil, coating side. When oil just begins to smoke, stir-fry ginger, white and pale green parts of scallions, and salt until fragrant, about 1 minute. Crumble rice into wok and stir-fry until lightly browned, 10 to 12 minutes. Remove from heat, then add scallion greens, pineapple, and sesame oil, tossing to combine. Season with salt.
