In 12-inch nonstick skillet, heat olive oil over medium-high heat. Add chicken, onion, salt, Italian seasoning, and pepper. Cook 4 to 5 minutes, turning occasionally, until chicken is no longer pink in center and browned. Reduce heat to medium.
Stir in tomatoes and frozen vegetables. Cover and cook 15 to 20 minutes or until vegetables are tender and heated through.
Sprinkle with cheese. Cover and cook 1 to 2 minutes or until cheese is melted.