Heat the olive oil in a large pot over medium heat. Add the flour and whisk constantly until the mixture turns a deep brown color to create a roux.
Add the onions, celery, and bell pepper to the pot, cooking until the vegetables are tender, about 5 minutes.
Stir in the garlic and cook for another minute until fragrant.
Add the sliced okra to the pot and cook for an additional 5 minutes.
Stir in the Cajun seasoning and chicken stock, bringing the mixture to a simmer.
Add the shrimp and crab meat into the pot and cook for another 10 minutes, or until the shrimp are cooked through.
Serve the gumbo hot over cooked rice.