Heat olive oil in a large pot or Dutch oven over medium heat.
Add the chopped onion, bell pepper, and celery (the 'holy trinity' of Cajun cooking). Sauté for about 5 minutes until the vegetables are softened.
Stir in the minced garlic and cook for an additional minute.
Add the soaked red beans, water or chicken broth, smoked sausage, ham hock (if using), thyme, Cajun seasoning, bay leaf, salt, and pepper. Bring to a boil.
Reduce the heat to low, cover the pot, and let it simmer for about 1.5 to 2 hours, stirring occasionally, until the beans are tender and creamy.
Taste and adjust the seasoning if necessary.
Once the beans are cooked, remove the ham hock or bacon. If using a ham hock, shred the meat and return it to the pot.
Serve the red beans over cooked white rice in bowls and garnish with chopped green onions.