In a large saucepan, bring 2 cups of water to a boil. Add the basmati rice, cover, and reduce heat. Cook as per the package instructions. Once done, set it aside.

Heat the vegetable oil in a large stockpot or Dutch oven over medium heat. Working in batches, add the sliced sausage, stirring frequently, until it is lightly browned, about 3–4 minutes. Remove the sausage and set aside.

In the same pot, add the diced onion, green bell pepper, and celery. Cook while stirring occasionally, until tender, about 3–4 minutes.

Stir in the tomato paste, minced garlic, and Cajun seasoning. Cook until fragrant, about 1 minute.

Add the red beans, chicken stock, hot sauce, bay leaf, and browned sausage back into the pot. Season with salt and pepper to taste. Bring the mixture to a boil, then cover and reduce the heat to simmer for 15 minutes.

Uncover the pot and continue to simmer until the mixture is slightly reduced, about 15 minutes more. Using a wooden spoon, mash some of the beans to thicken the sauce slightly, if preferred. Adjust the seasoning if needed.

Serve the red beans mixture immediately, topped with the prepared rice and garnished with fresh parsley, if desired.