In a small saucepan, combine the soy sauce, vinegar, garlic and bay leaf over medium-high heat. Heat the mixture until it just comes to a boil. Remove from the heat and set aside.
In a large saucepan, heat the olive oil over medium heat. Add the yellow onion and saute until soft and lightly golden, about 6 minutes. Add the chicken stock and bring to a boil. Add the soy sauce mixture, chicken and couscous. Return to a boil, reduce the heat to medium and simmer for 2 minutes. Add the bok choy and simmer until the bok choy is tender, about 2 minutes.
Discard the bay leaf. Ladle into warmed individual bowls and garnish with the green onions. Serve immediately.