The observation and characterisation of the Higgs boson represents the culmination of over forty years of experimental and theoretical progress, cementing the Standard Model (SM) as the most successful fundamental physical theory to date. However, many open questions still remain which can only be addressed with the new physics predicted by many beyond the SM (BSM) theories. Many such theories, such as two Higgs doublet models and the next Next-to-Minimal Supersymmetric Standard Model, also predict new light bosons or an extended Higgs sector. The observation of the Higgs boson opens a new window to search for such new particles, denoted a. This project aims to observe the production of new light hadronically decaying bosons in the Higgs boson decays h->Za, focusing on h->Za->ll+hadrons final states. This is breaking new ground as the h-> Za channel is entirely uncharted territory, only recently proposed, which will probe large parts of the currently allowed 2HDM parameter space. These searches have been out-of-reach to-date due to the challenge of reconstructing low-mass boosted hadronic objects. The exploitation of these channels will require significant innovations such as the development of new reconstruction techniques for boosted low mass hadronic resonances. Looking to the future the upgrade of the ATLAS Inner Tracker is of paramount importance to fully exploit the physics potential of this project with the High Luminosity LHC. The results of this project will represent an important step towards understanding the extent of the Higgs sector or lead to a revolutionary discovery, the first observation of BSM physics at the LHC.