Melt butter with olive oil in large skillet. Add chicken, tarragon and garlic (I wait to add the garlic until later to prevent burning it) and cook over medium heat until chicken is no longer pink, about 8 to 10 minutes.
In a small bowl, stir together orange juice concentrate,orange juice, cornstarch and reserved mandarin orange syrup. Stir into chicken mixture. Reduce heat to medium. Cook stirring frequently, until chicken is thoroughly cooked and tender and sauce has thickened, about 8 to 10 minutes. Stir in oranges and green onions. Serve with hot cooked pasta or rice.