Set a large pot to medium-high heat and add oil. Once hot, add ground chicken and cook until no longer pink, 6-8 minutes, crumbling with a spoon as it cooks. Drain and discard excess liquid, if any.
Reduce heat to medium. Add bell peppers, onion and garlic; cook for 5 minutes.
Add diced tomatoes, tomato sauce, chicken broth, Italian seasoning, salt and pepper. Bring to a boil, then reduce heat to low. Cover and simmer for 30 minutes.
Just before serving, stir in cooked brown rice. Ladle into individual serving bowls and sprinkle with parsley, if desired.