Raspberry Balsamic Glazed Chicken

1 teaspoon vegetable oil
Cooking spray
1/2 cup red onion, chopped
1/2 teaspoon dried thyme
1/2 teaspoon salt, divided
4 boneless, skinless chicken breast halves
1/3 cup seedless raspberry preserves
2 tablespoons balsamic vinegar
1/4 teaspoon pepper

Heat oil in nonstick skillet coated with cooking spray over medium high heat until hot. Add onion and saut