In a large skillet over medium heat, cook the Italian sausage, breaking it into small pieces. Cook until mostly browned, then drain off excess grease.
Add the cooked sausage, chopped vegetables, diced tomatoes, beans, broth, and all seasonings to the slow cooker. Stir until everything is well combined.
Cover and cook on high for 4–5 hours or on low for 6–8 hours, until vegetables are tender.
Serve hot, topped with shredded parmesan cheese and extra red pepper flakes, if desired.
Notes
This soup is even better the next day! Serve with crusty bread or a green salad for a complete meal.