Heat the oil in a pot over medium heat. Add the sausage and brown for 3 - 5 minutes, stirring occasionally.
Add the bell peppers, celery, onion, garlic, cajun seasoning, and thyme. Sauté for 6 minutes, stirring occasionally, until the onions are softened. Add in the flour and cook while stirring for 3 - 5 minutes until the flour starts to turn golden brown.
Add the crushed tomatoes and chicken broth. Stir to combine. Simmer for about 20 minutes, stirring occasionally. Add in the shrimp and cook for 5 minutes.
Season with salt and pepper to taste. Garnish with scallions and serve with rice and oyster crackers.