In a large pot, heat vegetable oil over medium heat. Gradually stir in the flour and cook, stirring constantly, until the mixture turns a dark brown color, about 20-30 minutes.

Add the diced onion, bell pepper, and celery to the roux. Sauté for 5-7 minutes until the vegetables soften.

Stir in the minced garlic, cajun seasoning, thyme, and bay leaf. Cook for an additional minute to release the flavors.

Slowly add the seafood or chicken stock, stirring constantly to prevent lumps. Bring the mixture to a boil.

Once boiling, add the sliced andouille sausage. Reduce the heat and let it simmer for 20 minutes.

Next, add the shrimp, crabmeat, and optionally the oysters. Simmer for another 10-15 minutes until the seafood is cooked through.

Remove the bay leaf and stir in sliced green onions and chopped parsley. Season with salt and pepper according to your preference.

Scoop hot gumbo into bowls over cooked white rice.