Heat oil in 12-inch nonstick skillet over medium heat until hot. Add onion; cook 4 to 5 minutes or until tender, stirring occasionally.
Add chicken; sprinkle with Cajun seasoning. Cook 6 minutes, stirring occasionally.
Add okra; cook an additional 2 to 4 minutes or until okra is thoroughly heated and chicken is no longer pink in center. Add tomatoes; cook and stir until thoroughly heated.