COMBINE tarragon, rosemary and pepper; spread evenly onto chicken. Melt 1 Tbsp. of the margarine in large skillet on medium heat. Add chicken; cook 6 to 7 min. on each side or until cooked through (170°F). Remove from skillet; cover to keep warm.
MELT remaining 1 Tbsp. margarine in same skillet. Add shallots; cook 1 to 2 min. or until tender, stirring occasionally. Add vinegar; cook 1 min. Stir in broth and sugar; bring to boil. Cook until sauce is reduced by one third, stirring occasionally. Stir in mustard.
MIX cornstarch and water until well blended. Add to ingredients in skillet; mix well. Bring to boil; cook until thickened, stirring occasionally. Serve spooned over the chicken.