Moving camera to center on clicked object?

I am trying to move my camera so that it’s directly on top of the game object that is clicked. I can already identify the game object that was clicked and get it’s position, the thing is I have the camera angled down 30 degrees, and you can zoom in and out (which moves the camera forward or back). I need to identify the position that the camera needs to move to so I can use an iTween to move the camera there. I was thinking I need to start and the object’s position and move along the Camera.Back vector until I hit camera’s Y coordinate, but I have no idea how to calculate it.
I hope it’s not confusing >_<

The clarification is helpful, though there are still parts of this question I cannot visualize. Given that you want to change XZ, I assume you are looking down? I can think of two approaches.

Approach #1 to construct a mathematical plane from the Unity’s Plane class. through the object. I’m guessing it would be parallel to the XZ plane. Then use Camera.ViewportPointToRay() to construct a ray from the center of the camera. With the Ray you can use Plane.Raycast() along with Ray.GetPoint() to find a world coordinate on the XZ plane where the camera is currently looking. Subtracting this position from the object position will give you the delta you need to move the camera to center the object.

Approach #2 is similar to #1 except to get the world point you would Camera.ViewportToWorldPoint() to find the position.