  Chirality is a fundamental asymmetry phenomenon, with chiral optical elements
exhibiting asymmetric response in reflection or absorption of circularly
polarized light. Recent realizations of such elements include nanoplasmonic
systems with broken mirror symmetry and polarization-contrasting optical
absorption known as circular dichroism. An alternative route to circular
dichroism is provided by spin-valley polarized excitons in atomically thin
semiconductors. In the presence of magnetic fields, they exhibit an imbalanced
coupling to circularly polarized photons and thus circular dichroism. Here, we
demonstrate that polarization-contrasting optical transitions associated with
excitons in monolayer WSe$_2$ can be transferred to proximal plasmonic
nanodisks by coherent coupling. The coupled exciton-plasmon system exhibits
magneto-induced circular dichroism in a spectrally narrow window of Fano
interference, which we model in a master equation framework. Our work motivates
exciton-plasmon interfaces as building blocks of chiral metasurfaces for
applications in information processing, non-linear optics and sensing.
