Heat 2 tablespoons of oil in a heavy-bottomed pot over medium heat (or 3–4 tbsp water for oil-free). Add diced celery, onion, bell pepper, minced garlic, and a generous pinch of salt; sauté until the onion is tender, about 4–6 minutes.
Add the soaked, drained beans and 8 cups of water to the pot. Increase heat to high and bring to a boil.
Stir in the kombu (if using), bay leaves, and dried thyme, then reduce heat to medium-low to maintain a gentle simmer.
Simmer uncovered for about 90 minutes, stirring occasionally; skim any foam and add more water if needed so the beans stay submerged. Check for doneness and continue simmering until beans are tender but intact.
While the beans simmer, cook the rice according to package instructions.
When the rice is nearly done, heat the remaining 2 tablespoons oil in a skillet over medium heat. Add the sliced vegan sausage and cook, stirring often, until golden brown, about 5–7 minutes.
When the beans are tender, remove from heat and stir in 1–2 bouillon cubes (to taste), smoked paprika, liquid smoke, and Cajun seasoning. Taste and adjust seasoning, adding a second bouillon cube if desired.
Stir the cooked vegan sausage into the beans, then serve the red beans over the cooked rice and garnish with chopped parsley. Serve hot.
Instant Pot option: Sauté the vegetables in 2 tbsp oil on Sauté, add beans, kombu, bay leaves, thyme and enough water or broth to cover by 1 cm (add bouillon if using water). Pressure cook on High 15 minutes, natural release 15 minutes, then finish by stirring in smoked paprika, liquid smoke, Cajun seasoning and sausage.