Called red peas in Jamaica, this ingredient connects this Jamaican soup with Africa's Caribbean diaspora.
Drain beans. Place in a large pot along with water, broth, chicken, scallions, celery, garlic, parsley, salt, pepper and thyme. Cover and bring to a boil over high heat; boil for 30 minutes. Reduce heat to a simmer and cook, stirring occasionally, until the beans are tender, about 1 hour. (Add water or broth if the soup seems too thick.)
Season the soup with more pepper, if desired. Ladle into bowls and garnish with sweet onion.