Combine first 3 ingredients in a small bowl. Combine salsa and tomatoes.
Place a large nonstick skillet coated with cooking spray over medium-high heat until hot. Add chicken, and sprinkle evenly with chili powder mixture. Top with pepper stir-fry and onion. Pour salsa mixture evenly over top. Bring to a boil; cover and reduce heat. Simmer 10 minutes or until chicken is done. Serve over cooked rice.