Make sauce ahead of time as follows: Mix chili
sauce, vinegar, horseradish, garlic and salt in a
bowl. Refrigerate. When ready to start cooking
chicken, pour half the sauce over the chicken breasts
in a shallow pan. Refrigerate for 5 - 10 minutes.
Preheat grill. Remove chicken from marinade. Discard
the marinade that the chicken was in. Place chicken
on the grill. Grill chicken, turning and basting
frequently with the reserved marinade for about 30
minutes or until juices run clear when meat is
pierced with a knife. Heat remaining marinade in a
small pan, stirring occasionally until heated
through. Serve chicken with sauce on the side.
Garnish with green onion, if desired.