Brown the tofu: Heat the oil in a nonstick skillet over medium-high heat. When the oil shimmers, add in the shredded tofu and spread it out in an even layer. Allow to cook for 3-5 minutes undisturbed, until the bottom is golden-brown. Give the tofu a toss and continue to pan-fry, stirring occasionally, for another 8-12 minutes, or until evenly golden brown. Pan-fry more or less depending on how chewy you want it to be. Set aside to cool while you prep your remaining ingredients.
Mix the sauce: While the tofu crisps, whisk together the grated onion, grated apple, soy sauce, toasted sesame oil, brown sugar, mirin, garlic, ginger, gochugaru (if using), and black pepper in a small bowl. (Alternatively, you can add all ingredients to a blender and purée.)
Glaze the tofu: When the tofu is browned to your preference, reduce the heat to medium-low. Stir in the white parts of the green onions, then pour the bulgogi sauce over the tofu and immediately stir to coat. Keep stirring constantly for 3-5 minutes to allow the soy glaze to reduce and caramelize. Finish with the green parts of the green onions and an extra sprinkle of toasted sesame seeds.