How to Make It
In a medium bowl, toss the pork loin with 1/4 teaspoon of the salt and the pepper. In a large frying pan or wok, heat 1 tablespoon of the oil over moderately high heat. Add half the pork and cook, stirring, until browned, 2 to 3 minutes. Remove. Repeat with another tablespoon of the oil and the remaining pork. Remove.
In a small bowl, combine the cornstarch and water. Heat the remaining 1 tablespoon oil in the pan. Add the onion, carrots, bok choy, garlic, and celery seeds. Cook, stirring, for 3 minutes. Stir in the broth and orange juice and bring to a simmer. Add the pork and any accumulated juices and the remaining 3/4 teaspoon salt and simmer until the meat is just done, 1 to 2 minutes. Add the cornstarch mixture and cook, stirring, until the sauce thickens, about 1 minute.