Trim breasts of excess fat. Using a mallet, gently pound flat the breast. Set aside.
Using a blender, mix egg whites and yogurt, and blend until smooth. Remove from blender and stir in vegetables. Spread thinly on top of breasts. Roll tightly in a pinwheel fashion. Secure with another layer of plastic film.
Simmer gently in the chicken stock over low heat for 35 minutes. Remove film and slice across the pinwheel to show the colors on the inside.