In a heavy-bottomed skillet, heat the olive oil over medium. Sauté the onions and garlic until the onions are translucent.
Add the ground beef and sausage to the skillet. Cook until browned, crumbling as it cooks. Add the onions, garlic, ground beef, and sausage to a 6 quart slow cooker.
Add the bell peppers, diced tomatoes, tomato sauce, beef broth, brown sugar, Italian seasoning, kosher salt, and pepper to the slow cooker. Stir to combine.
Cover and cook on low for 6-8 hours.
30 minutes prior to when you'd like to eat, add the white rice to the slow cooker.
Ladle the soup into bowls and top with shredded parmesan cheese.
Notes: I like to cut the bell peppers into big chunks so that they don't disintegrate into the soup while they cook. Use whatever color bell peppers that you'd like.