How do you instantiate an object rotated 90 is the y-axis?
Instantiate (object, position, Quaternion.Euler(0, 90, 0));
I did it with variables, and
pieceRotation = Quaternion.AngleAxis(270, Vector3.up);
Instantiate (transform.position, pieceRotation);
Just Instantiate it and then set its rotation after it is created.
instantiatedObject.transform.rotation = Quaternion.Euler(angleX, angleY, angleZ);