Heat the sesame oil in a large pot over medium heat. Add the pork cubes, season with salt and pepper, and brown on all sides for about 5 minutes.
Stir in the diced onion, minced garlic, and grated ginger. Cook for 2 minutes until the onion softens.
Pour in the soy sauce and chicken broth. Bring the mixture to a simmer, then reduce heat to low, cover, and cook for 25 minutes until the pork is tender.
Add the halved bok choy to the pot. Simmer uncovered for 5 minutes until the bok choy is bright green and slightly wilted.
Taste and adjust seasoning if needed. Ladle into bowls and top with sliced green onions.