In a large Dutch oven, brown the sausage and onion over medium heat until the sausage is no longer pink, 3 to 5 minutes. Drain off any grease from the pan.
Stir in the marinara sauce, broth, bell peppers, tomatoes, cabbage, garlic, vinegar and seasonings. Bring the soup to a boil, then reduce heat and simmer, covered, until the peppers are tender, 10 to 15 minutes.
If using quick-cooking rice, add the rice and cook for an additional 5 to 7 minutes, until the rice is tender. If using cooked rice, stir in the rice and there is no need to cook it further.
Ladle the soup into bowls. Garnish with freshly chopped parsley, if desired.
Notes
For a thinner soup, add in 1 to 2 additional cups of beef broth.