rotate object to face mouse cursor along global y axis

Hello, I am making a isometric tank game and I am trying to make the controller for the tank turret. I want to rotate the turret along the global y axis(or local z axis) so it will always face the mouse cursor with a bit of smooth rotation in between. I have tried many different methods but they all seem to result in the turret rotating oddly or along the wrong axis. I am new to scripting and not really sure what to do. Please help!