Slice the king oyster mushrooms into ¼-inch thick pieces. Halve extra-large mushrooms for even cooking.

In a mixing bowl, whisk together soy sauce, gochujang, mirin, sugar, minced garlic, and sesame oil until smooth.

Coat the sliced mushrooms thoroughly with the marinade. Let them marinate for at least 20 minutes in the fridge.

Heat a cast-iron pan over medium heat and add a splash of neutral oil. Cook the mushrooms in batches for 2-3 minutes on each side.

Once cooked, return all mushrooms to the pan, pour in remaining marinade, and cook until sauce thickens.

Serve hot over steamed rice, topped with cucumber, sesame seeds, and scallions. Optional: drizzle extra sesame oil.