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The nearly free electron metal next to a localized Mott insulating state has been recently proposed as a way to probe Kondo lattice physics and to gain insight into how the two extremes of localized and delocalized electron states interact (Sunko, et al, Science advances 6, 2020). Although high harmonic generation has been used extensively to investigate the gas phase, its extension to solids is relatively recent, and has not yet been applied to interfaces. Here, we investigate the field-induced dielectric break-down at the Mott-insulator/metal interface using high harmonic generation, emitted when the interface is subjected to an ultrafast laser pulse. We show that the intensity of high harmonic emission correlates closely with doublon production and the corresponding loss of short-range anti-ferromagnetic order. For strong interlayer coupling, the harmonic intensity is defined by a phase transition between states that do not exist in a pure Mott insulator case. For weak interlayer coupling, the threshold for dielectric breakdown is considerably lowered due to the presence of a metallic layer. This suggests that interlayer coupling can be used as an additional knob to control magnetic insulator break-down, with implications for using Mott insulators as memristors in neuromorphic circuits.