Project max value of field x-direction
 

I want a slice in the yz-plane which is colored by the maximum value of my field M in the x-direction, is there any way of doing this? M is a mass fraction between 0 and 1 calculated by OpenFOAM. The grid is irregular (made with snappyHexMesh), so it's not as easy as simply taking the maximum of the first dimension of the 3-dimensional array M.