Spray 3- to 4-quart slow cooker with cooking spray. Between pieces of plastic wrap or waxed paper, place each chicken breast smooth side down; beginning in center of breast, gently pound with flat side of meat mallet or rolling pin until about 1/4 inch thick.
Place 1/2 ham slice and 1/2 cheese slice on each breast. Roll up, folding in sides. Place rolls, seam sides down, in single layer in slow cooker. In medium bowl, mix remaining ingredients; spoon over chicken.
Cover; cook on Low heat setting 3 hours 30 minutes to 4 hours 30 minutes.
Remove rolls from cooker to cutting board. Beat sauce in cooker with wire whisk until smooth. Spoon about 1/3 cup sauce onto each of 6 plates. Cut each roll crosswise into thin slices; arrange on sauce.