Trim the ends off the green beans. You can also cut them in half if you prefer a shorter (easier to eat) bean.
Cook the bacon, drain and crumble it. Set it aside for use at the end.
Using the same pot still containing the bacon grease, add the onions and saute over medium heat until they soften, about 2-3 minutes.
Add the green beans and chicken stock and bring to a simmer.
Reduce heat, cover and simmer for 90 minutes.
Stir in the butter, Cajun seasoning and bacon at the end and add additional salt if needed.
Notes
Stir in the bacon after the green beans are done braising. Otherwise, you have soggy bacon which isn't very good.
Adjust the salt to taste. If you're using Cajun seasoning with salt, you likely will not need additional salt. Remember, the bacon stirred in at the end will also be salty.