Heat olive oil in a large pot over medium heat. Add onion and sauté for 2–3 minutes.
Add ground beef, breaking it apart with a spoon, and cook until browned. Drain excess fat.
Stir in bell peppers and garlic. Cook for another 2–3 minutes.
Add diced tomatoes, tomato sauce, beef broth, basil, oregano, salt, and pepper.
Bring to a boil, then reduce heat and simmer uncovered for 25–30 minutes, stirring occasionally.
Stir in cooked rice and simmer for 5 more minutes. Adjust seasoning if needed.
Serve hot, garnished with parsley or cheese if desired.