Make the roux: In a large heavy pot, whisk together flour and oil over medium heat. Stir constantly until the mixture turns a deep brown, about 15–20 minutes. Be careful not to burn it.
Cook the vegetables: Add onion, bell pepper, celery, and garlic. Cook until softened, about 5 minutes.
Add okra: Stir in sliced okra and cook until it loses some of its stickiness, about 10 minutes.
Add stock and seasonings: Slowly whisk in the seafood stock. Add bay leaf, thyme, cayenne, paprika, salt, and black pepper. Simmer uncovered for 30–40 minutes, stirring occasionally.
Add seafood: Stir in the shrimp and crabmeat. Cook until the shrimp are pink and opaque, about 5 minutes.
Finish and serve: Remove the bay leaf. Garnish with parsley and green onions. Serve hot over white rice.
