  Graphene-based moir\'e superlattices have recently emerged as a unique class
of tuneable solid-state systems that exhibit significant optoelectronic
activity. Local probing at length scales of the superlattice should provide
deeper insight into the microscopic mechanisms of photoresponse and the exact
role of the moir\'e lattice. Here, we employ a nanoscale probe to study
photoresponse within a single moir\'e unit cell of minimally twisted bilayer
graphene. Our measurements reveal a spatially rich photoresponse, whose sign
and magnitude are governed by the fine structure of the moir\'e lattice and its
orientation with respect to measurement contacts. This results in a strong
directional effect and a striking spatial dependence of the gate-voltage
response within the moir\'e domains. The spatial profile and carrier-density
dependence of the measured photocurrent point towards a photo-thermoelectric
induced response that is further corroborated by good agreement with numerical
simulations. Our work shows sub-diffraction photocurrent spectroscopy is an
exceptional tool for uncovering the optoelectronic properties of moir\'e
superlattices.
