In a skillet over medium heat, brown the ground beef with the diced onion until the beef is fully cooked and onions are translucent.

Drain any excess fat from the beef and onion mixture and transfer to a 6-quart slow cooker.

Add the diced tomatoes (with their juice), chopped green bell peppers, tomato sauce, beef broth, dried basil, and dried oregano to the slow cooker.

Stir to combine all the ingredients well.

Cover the slow cooker and set it to cook on low for 6-8 hours, allowing the flavors to meld together.

About 30 minutes before serving, stir in the cooked rice and allow it to heat through.

Serve the soup warm with your choice of toppings, such as shredded cheese or sour cream.