The first step in the process is to change the normal vector in the "MapToPlane" module.  Since we want an XZ cut we need to make y normal direction by setting [0 1 0] as the input value.  Next you'll need to connect a "Scalar" module to the left most input tab of a "Compute" module.  In the "Compute" module set the Expression field to a*[0,1,0] which will multiply the scalar input value times in the vector to define a starting point for the cut plane.