As the rice cooks, heat oil in a small skillet until hot but not smoking. Add onion and toss to coat with oil. Cook, stirring constantly for 1 minute. Reduce heat and continue to cook, stirring often, until onion is soft, about 8 minutes. Raise heat to medium. Add garlic, celery, mushrooms and curry. Continue to cook, stirring frequently, until mushrooms have softened, about 8 minutes. Stir in apple juice and cook just to blend.