HEAT grill to medium-high heat.
MIX preserves and mustard in microwaveable bowl. Microwave on HIGH 30 to 45 sec. or until warmed. Stir in 1 Tbsp. tarragon. Add 2 Tbsp. preserves mixture to dressing; mix well. Set aside for later use.
GRILL chicken 7 min. or until done (165ºF), turning after 4 min. and brushing occasionally with remaining preserves mixture.
TOSS greens with couscous, nuts, apricots and onions in large bowl. Add dressing mixture; mix lightly. Serve with chicken.