Multidimensional FFT with mixed directions
if I understood it right, given your 3D volumetric data $x[m,n,p]$, first you want to take a 2D forward DFT (via 2D FFT) in the first two variables $m,n$ (i.e., for each m-n plane along 3rd dimension) and then take a 1D inverse DFT of vectors along the third dimension. 

Note that in the first operation you replace each data plane with frequency plane and create a new volumetric data, then you will be taking inverse DFT of this resulting volume, the MATLAB/OCTAVE code below demonstrates a simple example:

A = zeros(2,2,3);      % create a 3D data array
A(:,:,1) = [1,2;3,4];  % first plane of 3D data
A(:,:,2) = [1,2;3,4];  % second plane of 3D data
A(:,:,3) = [1,2;3,4];  % third plane of 3D data

B = fft2(A)        % it'll take 2D-DFT independently for each plane of A

C = ifft(B,[],3)  % we indicate that ifft() be taken along 3rd dimension...


As you can see, since after the first step we have same frequency data for each plane of B, the third step produced impulses for each vector of C along 3rd dimension, due to inverse DFT.

I believe this is easy enough? But still in two steps (you can merge them into one line but still two calls)...