1. Preheat olive oil in a large skillet on Medium-high heat.
2. Add red onion and sauté for 4-5 minutes.
3. Add chicken breast filets and cook for 6 to 7 minutes on each side.
4. Remove chicken from skillet and keep warm. Reduce heat to Medium.
5. Add raspberry preserves and balsamic vinegar. Stir constantly until well blended and bubbly.
6. Drizzle over chicken and serve immediately.