Heat oil in medium skillet over medium-high heat. Sprinkle chicken with 1/8 teaspoon salt. Place chicken in skillet and cook 12 to 15 minutes or until no longer pink in centers (165°F), turning once. Remove from skillet; keep warm.
Add onion to skillet; cook and stir 5 minutes or until tender. Add undrained tomatoes; simmer 5 minutes or until slightly thickened. Stir in pesto and remaining 1/8 teaspoon salt just before serving over chicken.