In a large saucepan of 2 cups water, cook rice according to package instructions and set aside.
Heat vegetable oil in a large stockpot or Dutch oven over medium heat.Working in batches, add sausage and cook, stirring frequently until sausage is lightly browned, about 3 to 4 minutes.Set aside.
Add onion, bell pepper, and celery.Cook, stirring frequently until tender, about 3 to 4 minutes.
Stir in tomato paste, garlic, and Cajun seasoning until fragrant, about 1 minute.
Stir in red beans, chicken stock, hot sauce, bay leaf, and sausage.Season with salt and pepper to taste.
Bring to a boil and cover and reduce heat and simmer for 15 minutes.Uncover and continue to simmer until reduced, an additional 15 minutes.
Using a wooden spoon, mash beans until slightly thickened.If desired, season with salt and pepper, to taste.
Serve immediately topped with rice and garnished with parsley, if desired.
