If pickled onions are desired, in large nonreactive bowl, stir together onions and lime juice. Cover tightly; refrigerate 1 hour.
In 10-inch skillet, heat shredded chicken and cooking sauce over medium heat to simmering. Cook about 5 minutes or until hot and chicken begins to fall apart in sauce. Remove from heat.
Spoon 1/3 cup chicken mixture into each taco shell. Top with cheese and pickled onions. Serve lime wedge on the side.