Alloy nanoparticles are characterized by the combination of multiple interesting properties which are attractive for technological and scientific purposes. A frontier topic of this field is represented by nanoalloys with composition not thermodynamically allowed at ordinary temperature and pressure (i.e. metastable), because they require out-of-equilibrium synthetic approaches. Recently, laser ablation synthesis in solution (LASiS) has been successfully applied to the realization of metastable nanoalloys thanks to the fast kinetics of nanoparticles formation. However, the role played by the chemical environment on the final composition and structure of laser generated nanoalloys still has to be fully elucidated. Here we investigated the influence of different synthetic conditions on the LASiS of metastable nanoalloys composed by Au and Fe, such as the use of water instead of ethanol, the bubbling of inert gases and the addition of few vol% of H2O2 and H2O. The two elements showed different reactivity when LASiS was performed in water instead of ethanol, while minor effects are observed by bubbling pure gases such as N2, Ar and CO2 in the liquid solution. Besides, the plasmonic response and the structure of nanoalloys was sensibly modified by adding H2O2 to water. We also found that nanoparticles productivity is dramatically influenced just by adding 0.2% of H2O in ethanol. These results suggest that the formation of a cavitation bubble with long lifetime and large size during LASiS is useful for the preservation of metastable alloy composition, whereas an oxidative environment hamper the formation of metastable alloy nanoparticles. Overall, by acting on the type of solvent and solutes, we were able to switch from a synthetic approach conservative for the compostion of Au-Fe nanoalloys to a reactive environment which gives unconventional structures such as metal@iron-oxide nanoshells and nanocrescents of oxide supported on metal nanospheres. These results expand the knowledge about the mechanism of formation of nanoalloys by LASiS, and show how to obtain multielement nanoparticles of huge interest for nanomedicine, plasmonics, magneto-plasmonics and catalysis.