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1
Combine the soy sauce, sugar, sesame oil, garlic, ginger, and Asian pear juice in a bowl and stir until the sugar dissolves. Add the thinly sliced beef, turning to coat every surface. Cover and refrigerate for a minimum of 4 hours and a maximum of 24; beyond 24 hours the pear's enzymes over-tenderise the fibres and the texture deteriorates. The marinade is ready when the sugar is fully dissolved and the beef has taken on a deep amber coat.
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2
Stir the gochujang into the mayonnaise until uniform in colour and smooth. Combine the chopped cilantro and diced onion in a separate small bowl. Both can be prepared during the marinating period and held, covered, in the refrigerator.
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3
This is where the dish lives or dies. Bring a flat-top griddle or heavy cast-iron pan to the highest heat the burner will produce. Add the marinated beef in a single, uncrowded layer — work in batches rather than crowd the pan, which would steam rather than sear the meat. The sugar in the marinade must caramelise against the metal: listen for an immediate, aggressive sizzle when the beef makes contact, and look for the edges to brown and char within 60–90 seconds per side. The finished slices are dark at their edges, glossy at their centres, and carry the sweet-smoky char that defines the dish.
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4
Warm the corn tortillas directly over a gas flame or on a dry griddle, 20–30 seconds per side, until they are pliable and carry faint char spots. Double each tortilla — lay two together — before filling. The doubled tortilla should feel supple, not brittle, when folded.
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5
Lay slices of seared bulgogi across each doubled tortilla. Top with a spoonful of chopped kimchi, a pinch of cilantro-onion relish, and a drizzle of gochujang-mayo. Finish with a squeeze of lime over each assembled taco immediately before serving. The taco is ready when it presents all four elements simultaneously: sweetness from the caramelised beef, sourness from the kimchi and lime, heat from the gochujang, and freshness from the cilantro.