In a shallow dish. Combine oil, lemon juice and pepper. Add chicken and turn to coat with marinade. Marinate, turning occasionally, for 30 minutes. Meanwhile, combine vinegar, wine and tarragon in saucepan. Boil until reduced to about 2 tablespoons. Reduce heat to low, add butter and mustard and stir until butter melts. Set sauce aside; keep warm. Drain chicken well, grill or broil over medium heat, turning once and basting frequently with mustard sauce, until just cooked through about 5 minutes aside. Be careful not to overcook chicken. Serves 6.