1 Cut the pork with the grain into 2-inch-wide strips. Then cut each strip across the grain into 1/4 inch-thick slices.
2 Place the pork slices in a bowl. Add 1 tablespoon each of the oil, soy sauce and cornstarch. Mix gently until the pork is well coated.
3 Cut the bell pepper into 1-inch squares. Cut the scallions into 2-inch lengths. Slice the ginger (if using).
4 In a bowl, stir together the broth, ketchup, orange zest (if using) and the remaining 2 teaspoons cornstarch and 1 tablespoon soy sauce.
5 In a large skillet or wok, warm 1 tablespoon of the oil over medium-high heat. When the oil is very hot but not smoking, add the pork and the marinade and stir-fry until the pork is almost completely browned but still slightly pink in the center, 3 to 4 minutes. Using a slotted spoon, transfer the pork to a plate and set aside.
6 Add the remaining 1 tablespoon oil to the skillet. Add the bell pepper, scallions and ginger, and stir-fry until the scallions wilt, 3 to 4 minutes.
7 Return the pork to the skillet. Stir the broth mixture, then stir it into the skillet. Bring the liquid to a boil.
8 Add the oranges and cook, stirring contantly, until the vegetables are crisp-tender and the pork is cooked through, 2 to 3 minutes. Discard the ginger slices before serving.