Trying to Lerp knock-back on Character Controller

Hey guys.

I'm trying to Lerp and smooth out a movement for my melee weapons. Its a top-down shooter style game.

Here's my melee script.

     public void OnTriggerEnter(Collider other) 
     {
         Vector3 dir = other.transform.position - transform.position;
         dir.y = 0;
 
         if (other.rigidbody) 
         { 
             if(swinging)
             {
                 other.rigidbody.AddForce (dir.normalized * force);
             }
         }
 
         if (other.gameObject.tag == "Enemy") 
         {
             var aiHealth = other.gameObject.GetComponent<ZombieDeathScript>();
 
             if(swinging)
             {
                 CharacterController controller = other.gameObject.GetComponent<CharacterController>();
                 aiScript = other.gameObject.GetComponent<AIFollow>();
 
                 Vector3 bashDir = other.transform.TransformDirection(Vector3.back);
 
                 other.transform.position = Vector3.Lerp(transform.position, transform.position + bashDir, pushSpeed);
                 //controller.SimpleMove(bashDir * Time.deltaTime * pushSpeed);
 
                 aiScript.speed = 2.5f;
                 aiHealth.health -= damage;
                 audio.clip = sounds[Random.Range(0,sounds.Length)];
                 audio.Play();
                 Invoke("ResetSpeed", 2);
             }
         }
     }
 
     void ResetSpeed ()
     {
         aiScript.speed = 5;
     }

The problem is, the knock-back is instant, I want it to knock the enemy back slowly. The enemies use Character Controllers, I had them as rigidbodies before, but recently changed. And that's why I'm asking for some help. :)