Heat oil in Dutch oven or large saucepan over medium-high heat until hot. Add chicken, onions and garlic; cook and stir 5 minutes or until chicken is browned and onions are tender.
Stir in tomatoes, peanut butter, chili powder, salt and red pepper flakes. Bring to a boil. Reduce heat; cover and simmer 35 minutes. Serve over rice; sprinkle with peanuts.