Cook rice according to package directions, omitting salt and fat.
Heat a large Dutch oven over medium-high heat. Coat pan with cooking spray. Add onion and garlic; sauté 3 minutes. Add broth and potato; bring to a boil over medium-high heat. Cover, reduce heat, and simmer 5 minutes or until potato is tender.
Combine milk and flour, stirring well with a whisk. Add the milk mixture to potato mixture; cook 5 minutes or until slightly thick, stirring constantly. Remove from heat; add cheese, stirring until cheese melts. Stir in rice, chicken, pepper, and salt. Garnish with parsley, if desired.