1. Coat a large nonstick skillet with cooking spray; place over medium heat until hot. Add chicken, and cook 7 minutes on each side or until done; set aside, and keep warm.
2. Melt margarine in a saucepan over medium heat. Add flour, and cook 1 minute, stirring constantly with a wire whisk. Gradually add evaporated milk to flour mixture, stirring constantly. Stir in chives. Reduce heat to medium-low, and cook 3 minutes or until thickened and bubbly, stirring constantly. Add feta cheese, and stir until cheese melts. Spoon cheese sauce over chicken. Yield: 6 servings (serving size: 1 chicken breast half and 1/4 cup sauce).