There are many reasons to consider perturbative QFT around curved backgrounds, but it is often difficult to perform explicit computations in these settings. Progress in the study of scattering amplitudes (around a trivial background) suggests alternative perspectives to space-time Lagrangians and Feynman rules which could enable progress in the study of scattering on curved backgrounds. I will discuss one such alternative, known as double copy, with a particular focus on gluon and graviton scattering around non-linear plane wave backgrounds