In a large heavy-bottomed pot, combine ½ cup of all-purpose flour and ½ cup of vegetable oil over medium heat. Stir constantly for 15–30 minutes until the mixture darkens to a deep brown color.

Add 1 chopped onion, 1 chopped bell pepper, 1 chopped celery stalk, and 3 minced garlic cloves to the roux. Cook for about 5–7 minutes until the vegetables are tender and fragrant.

Gradually stir in 4 cups of seafood stock into the vegetable mixture, ensuring there are no lumps. Stir continuously for about 2–3 minutes until the mixture is smooth and starts to thicken.

Mix in 1 tablespoon of Cajun seasoning, 1 teaspoon of salt, ½ teaspoon of black pepper, and 2 cups of diced tomatoes. Bring the mixture to a boil, then reduce the heat to low. Allow to simmer for 20–30 minutes.

Once the sauce has thickened, add 1 pound of peeled and deveined shrimp. Cook for about 5 minutes, until the shrimp turn pink and opaque.

Just before serving, stir in ¼ cup of chopped green onions and ¼ cup of fresh parsley.

Ladle the rich sauce over a bed of cooked rice and serve hot.