Smoothly stop rotating

Right now I am casting out a ray to hit a enemy, while I have the enemy targeted I want my UI image to rotate, but when the ray moves off the enemy I want the rotation to return smoothly back to it's original position. I have tried to get Lerp to work in this case but I haven't had any success. So how can I take the rotation from after I have target the enemy and then smoothly rotate back to the starting position?

     void Update() 
     {
         Ray ray = Camera.main.ViewportPointToRay(new Vector3(0.5F, 0.5F, 0));
         
         Debug.DrawRay(ray.origin, ray.direction * 100, Color.yellow);
         
         RaycastHit hit;
         if (Physics.Raycast(ray, out hit))
         {
             if (hit.collider.tag == "Enemy")
                 {
                 reticle.color = Color.Lerp (reticle.color, targetColor, transitionTime * Time.deltaTime);
                 transform.Rotate(0, 0, speed * Time.deltaTime, Space.Self);
                 }
         }
         else
             {
             reticle.color = Color.Lerp (reticle.color, Color.white, transitionTime * Time.deltaTime);
             }
     }