Recent observations by the H.E.S.S. collaboration of the Galactic Centre region have revealed what appears to be gamma -ray emission from the decay of pions produced by interactions of recently accelerated cosmic rays with local molecular hydrogen clouds. Synthesizing a 3-D hydrogen cloud map from the available data and assuming a diffusion coefficient of the form \kappa(E) = \kappa0(E/E0)^ delta , we performed Monte Carlo simulations of cosmic ray diffusion for various propagation times and values of \kappa0 and delta . By fitting the model gamma -ray spectra to the observed one we were able to infer the value of the diffusion coefficient in that environment (\kappa = 3.0 +/- 0.2 kpc2Myr-1 for E = 1012.5eV and for total propagation time 104 yr) as well as the source spectrum (2.1 <= gamma <= 2.3). Also, we found that proton losses can be substantial, which justifies our approach to the problem.