Preheat oven to 350°; spray rimmed baking pan with cooking spray.
Slice chicken breasts horizontally in half, but do not cut all the way through. Open chicken breasts and spread fl at, cut side up; cover each with 1 slice each ham and cheese.
Fold chicken breasts to enclose filling; place on prepared pan. Brush chicken with oil; sprinkle with thyme and ¼ teaspoon pepper. Bake 30 minutes or until internal temperature of chicken and filling reaches 165°; let stand 5 minutes.
In small bowl, whisk mustard, honey and vinegar. Serve chicken drizzled with mustard mixture garnished with arugula, if desired.
Serving Size 1 breast
Servings 0
* Percent Daily Values are based on a 2,000 calorie diet. Your daily value may be higher or lower depending on your calorie needs.