Interactions between meso-scale eddies and the mean flow influence the fate and transport of momentum and of active and passive scalars in the ocean, such as heat, salt, CO2 and nutrients, and play a fundamental role in ocean-atmosphere interactions, ocean circulation, ocean-cryosphere interactions and the climate system. Their representation in ocean general circulation models is a critical component of a robust and reliable climate model. We present recent developments in diagnostics and representation of multi-scale eddy-mean flow interactions using the Eliassen and Palm flux tensor in an ocean general circulation model. These diagnostics shed light into the exchange of momentum and available potential energy and kinetic energy between the eddy field and the mean flow. This insight is used to inform parameterization of eddy-mean flow interactions in simulations that do not resolve meso-scale eddy activity in ocean general circulation models. Further, we discuss how the Eliassen and Palm flux tensor can be used to parameterize eddy-mean flow interactions. The developments presented are implemented in the ocean component of the Model for Prediction Across Scales, MPAS-O (http://mpas-dev.github.io), a novel ocean general circulation model that uses an unstructured C-grid in the horizontal.