We study the effect of thermal oxygen exposure on a monolayer of h-BN grown on vicinal Ni surfaces by scanning tunneling microscopy, X-ray absorption, and photoemission spectroscopies. Using a curved Ni crystal, we carry out a systematic exploration of the h-BN monolayer interfacing a full variety of vicinal orientations around the (111) high-symmetry direction. We demonstrate the occurrence of two processes upon oxygen exposure: oxygen intercalation underneath the h-BN layer, which leads to decoupling of the h-BN from the substrate, and oxidation of h-BN itself, which proceeds via substitution of nitrogen atoms. Oxygen intercalation appears to be substrate orientation dependent, while oxidation of h-BN is rather uniform over the different vicinal planes. These findings will be of importance for future applications of BN-based devices and materials under ambient conditions. ©