Lerp a Object along X and Z axis only.

 using UnityEngine;
 using System.Collections;
 
 public class Test : MonoBehaviour {
 
     public Vector3 startPos;
     public Vector3 endPos;
     public GameObject gameObjectOne;
     float angleT;
     float distanceH;
     Vector3 pointThree;
     float x;
     bool moveObjectPosOne,moveObjectPosTwo;
 
     public int speed;
     IEnumerator Start () {
         moveObjectPosOne = false;
         moveObjectPosTwo = false;
         yield return StartCoroutine(CalculateVariables());
     }
 
     double DistanceBetweenPoints(Vector3 vectorOne, Vector3 vectorTwo) {
          double distance = Vector3.Distance(vectorOne, vectorTwo);
          return distance;
     }
 
     
     float GetAngleBetweenPoints(Vector3 vectorOne, Vector3 vectorTwo) 
     { 
         float xDiff = vectorTwo.x - vectorOne.x; 
         float yDiff = vectorTwo.z - vectorOne.z; 
         return Mathf.Atan2(yDiff, xDiff) * (180 / Mathf.PI); 
     }
 
     float CalculateX(float angle, float distance) 
     {
         float x = distance * Mathf.Cos(angle);
         return x;
     }
 
     IEnumerator CalculateVariables() {
         gameObjectOne.transform.position = startPos;
         angleT = GetAngleBetweenPoints(startPos, endPos);
         distanceH = (float)DistanceBetweenPoints(startPos, endPos);
         x = CalculateX(angleT, distanceH);
         pointThree = new Vector3(startPos.x - x, startPos.y, startPos.z);
         yield return null;
     }
     
     // Update is called once per frame
     float VecOne;
     float VecTwo;
     void Update () {
         VecOne = Vector3.Distance(gameObjectOne.transform.position,pointThree);
         if (moveObjectPosOne) {
             gameObjectOne.transform.position = Vector3.MoveTowards(gameObjectOne.transform.position, pointThree, speed * Time.deltaTime);
             if (VecOne <= 0) 
             {
                 moveObjectPosOne = false;
                 moveObjectPosTwo = true;
             }
         }
         if (moveObjectPosTwo)
         {
             gameObjectOne.transform.position = Vector3.MoveTowards(gameObjectOne.transform.position, endPos, speed * Time.deltaTime);
             
         }
 
     }
 }

Sixth grade algebra. I have cooked this up real quick. Not sure if this would work exactly but you can start here. Hopefully I am not doing homework. :D