In a stockpot, sauté onion and sausage in olive oil until sausage is lightly browned, add garlic, green and red bell peppers. Sauté an additional 2 minutes. Add remaining ingredients and bring to a boil. Reduce heat to a low simmer. Cover and cook for 2 to 3 hours until beans are tender, stirring occasionally. Serve with grated Parmesan cheese and crusty Italian bread.