Add the remaining 1 tablespoon oil, scallion whites, ginger and chili-bean sauce (or chile-garlic sauce) to the pan. Add pork and cook, crumbling with a wooden spoon, until no longer pink, 3 to 5 minutes. Add broth, tamari (or soy sauce) and sugar. Mix cornstarch and water in a small bowl and add to the pan. Bring to a boil and cook, stirring, until slightly thickened, about 1 minute. Stir in the reserved noodles and bok choy; cook, stirring, until heated through, about 1 minute. Serve topped with scallion greens and crushed red pepper, if desired.