We present a theoretical study of mid-infrared (MIR) photodetection using planar graphene–insulator–graphene (GIG) tunnel junctions enhanced by electric field confinement due to plasmonic resonance. Nanopatterned graphene nanoribbons (GNRs) with lateral nanogap support localized plasmon resonances, yielding strong localized electric field enhancement (∼50×) at the gap edges. This enhances tunneling probability and leads to nonlinear I–V characteristics under IR excitation. Finite-element simulations reveal a photocurrent enhancement of ∼300× over monolayer graphene sheets, with response times in the sub-nanosecond regime. The GNR–GIG platform combines quantum tunneling and plasmonic field localization, offering a compact, high-speed MIR detection architecture synergistically combining advanced 2D material physics with nanoscale plasmonic engineering.