PLACE cilantro, evaporated milk, water and bouillon in blender; cover. Blend until smooth.
MELT butter in medium saucepan over medium heat. Remove from heat. Stir in flour, stirring constantly until smooth. Stir in cilantro mixture. Cook over medium-low heat, stirring constantly, until mixture comes to a boil and thickens slightly. Season to taste with pepper.
POUR sauce over chicken breasts.