Heat oil in large skillet on medium heat. Add chicken; cook and stir 3 to 5 minutes or until no longer pink. Stir in in Seasoning Mix and water. Bring to boil. Reduce heat to low; simmer 5 to 7 minutes or until most of liquid is absorbed and chicken is cooked through, stirring occasionally. Spoon into warm taco shells. Serve with desired toppings.