Cook white rice and set aside.
Heat vegetable oil in a Dutch oven over medium heat. Add sausage and cook, stirring frequently, until the sausage is lightly browned. Remove to bowl and set aside.
Add onion, bell pepper and celery. Cook, stirring occasionally until tender. Stir in tomato paste, garlic and Cajun seasoning until fragrant, about 1 minute. Stir in red beans, chicken stock, hot sauce and bay leaf. Add back sausage.
Bring to a boil, cover, reduce heat, and simmer for 15 minutes. Uncover and continue to simmer until reduced, another 15 minutes. In order to thicken the dish, transfer a portion of the beans (without the sausage) to a blender and blend until smooth. Add back to the pot. Season with salt and pepper to taste.
Serve topped with rice and garnished with parsley, if desired.