MycoBoard engineers the fungus Neurospora crassa to grow flat hyphal mats that function as biodegradable, breadboard-like electronic substrates. Overexpression of the metallothionein gene cmt drives silver ion capture and reduction into conductive nanoparticles along hyphal walls, making the fungus an active circuit architect of the object itself. Mats grown in molds guide the hyphal geometry via its thigmotropism, and conductive tracks are applied via stamp or screen print to emulate the typical Breadboard. The result decomposes in soil within weeks or months, unlike conventional FR4 fiberglass PCBs that contribute to the ongoing e-waste crisis.