Heat a large pot over medium heat. Working in batches, add sausage, and cook, stirring frequently, until sausage is lightly browned, about 3-4 minutes; remove and set aside.
Add in the oil and butter then the onion, bell pepper and celery. Cook, stirring occasionally, until tender, about 3-4 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; cover, reduce heat and simmer for 15 minutes. Uncover; add the smoked turkey leg and continue to simmer until reduced, an additional 15 minutes.
Remove the bay leaf. 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 green onion or parsley, if desired.