Make a roux with the flour and oil over medium heat. Stir it constantly while cooking until it's the color of chocolate ice cream.
When the roux is the right color, remove it from the heat and stir in the onions, celery, and bell pepper. Keep stirring until all the vegetables are soft. Then add the garlic, Creole seasoning, and salt, plus about 1/4 cup of the chicken stock. Stir until blended and set aside to cool.
In a medium-large saucepan, bring the remaining chicken stock to a simmer with the bay leaves and crab boil. Let it simmer for two or three minutes. Remove the bay leaves.
Spoon the roux into the chicken stock and stir with a whisk until completely blended. Let the mixture cook for a five minutes, then add the chicken meat.
Continue to cook, covered, on low heat for another 10-15 minutes. (You could also put the mixture into a slow cooker and let it cook for as long as an hour.)
Serve with or without rice. Garnish with the chopped green onions.