What is the best method of creating an element in a 3D environment along a specific axis?

I have a 3D space. When a user clicks their mouse I want to drop an item at a fixed Y and Z coordinate, but a variable X coordinate, relative to where the user clicked.

Please see the following image.

When the user clicks I want to drop a block onto the seesaw shape from a fixed height.

I can achieve this by creating a transparent plane in front of the seesaw and firing a ray cast at it, this will give me a good X coordinate to place on. The Y and Z coordinates are hard-coded, so aren't an issue (I want it to always fall from the same height). However, it seems like a very inefficient way to do something quite simple.

What is the best method of achieving this?

Below is my code that works using a ray cast. I don't have a transparent plane in the foreground, so it only works if I click on the actual seesaw. Clicking anything else makes the ray collide with trees in the background, which gives me coordinates that are way off.

using System.Collections; using System.Collections.Generic; using UnityEngine;

 public class clickBehaviour : MonoBehaviour
 {
 
     public GameObject GameCube;
     Ray ray;
     RaycastHit hit;
 
     // Update is called once per frame
     void Update()
     {
 
         
         ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         if (Physics.Raycast(ray, out hit))
         {
 
             if (Input.GetButtonDown("Fire1"))
             {
                 GameObject obj = Instantiate(GameCube, new Vector3(-75, 9, hit.point.z), Quaternion.identity) as GameObject;
                 Debug.Log(hit.point);
             }
 
         }
     }
 }

In this scene the Z axis is left to right.