Abstract: ATLAS has measured the production of di-jets in proton-led nucleus collisions at small scattering angles with respect to the proton beam. This measurement probes for possible saturation effects in the gluon distribution at small x-Bjorken. The talk will review existing experimental information on the gluon distribution in nucleons and nuclei, introduce measurements of forward di-jets as a probe of nuclear parton structure at the lowest x possible, and present the latest ATLAS di-jet measurement in p-Pb.