Heat oil in non-stick skillet coated with cooking spray over medium high heat until hot. Add onion and sauté 5 minutes. Combine thyme and 1/4 tsp salt; sprinkle over chicken. Add chicken to skillet and sauté 6 minutes on each side or until done. Remove chicken from skillet and keep warm. Reduce heat to medium-low. Add 1/4 tsp salt, preserves, vinegar, and pepper, stirring constantly until the preserves melt. Spoon sauce over chicken.