If using dried beans, sort and rinse them, then soak overnight or quick-soak by boiling 2 minutes and letting sit 1 hour.
Drain soaked beans and set aside.
Heat oil in a large pot over medium heat; add sausage (if using) and brown, then remove and reserve.
Add onion, celery and bell pepper; sauté until soft, about 6–8 minutes.
Stir in garlic, smoked paprika and thyme; cook 1 minute until fragrant.
Add drained beans, bay leaf and stock; bring to a boil.
Reduce heat, cover partially and simmer gently 60–90 minutes until beans are tender, stirring occasionally.
If beans break down too much, mash a few against the pot to thicken; add reserved sausage back in and adjust consistency with cooking liquid.
Meanwhile cook rice separately according to package directions; keep warm.
Season beans with salt and pepper to taste; remove bay leaf and spoon over rice, garnish with green onions or parsley, and serve.