In 10-inch nonstick skillet, heat oil over medium heat. Add chicken; cook 4 minutes. Turn chicken; add onion. Cover; cook 3 minutes, stirring occasionally.
Stir in remaining ingredients. Reduce heat to medium-low; cover and cook 5 minutes longer or until onion is crisp-tender, vegetables are hot, and juice of chicken is clear when center of thickest part is cut (170°F). If desired, season to taste with salt and pepper.