Heat vegetable oil in a large pot or Dutch oven over medium heat. Add sausage, onion, capsicum and celery. Cook, stirring occasionally until tender, about 3-4 minutes.
Stir in tomato paste, garlic and Cajun seasoning and cook for 1 minute or until fragrant.
Stir in beans, chicken stock, tabasco sauce (optional) and bay leaf. Season with salt and pepper, to taste. Bring to a boil, then cover and reduce heat to simmer for 15 minutes. Uncover and continue to simmer for an additional 15 minutes or until reduced.
Using a wooden spoon, mash beans until slightly thickened if desired. Season with salt and pepper to taste.
Remove bay leaves and serve immediately, topped with a little cooked white rice and garnished with parsley, if desired.