Rinse the 300g of rice in several changes of cold water until the water runs mostly clear, then drain well. Cook it by your usual method, in a rice cooker or a covered saucepan with the water it needs, until the grains are tender and fluffy. Start it first so it finishes while the pork marinates, then keep it covered and warm. The rice should be hot and ready before the pan goes on. That timing is what lets the pork go straight from the pan to the plate, since jeyuk bokkeum is at its best served immediately.

If the 700g of pork is not already thinly sliced, freeze it for 20–30 minutes until firm, then slice it as thinly as possible across the grain. In a large bowl, stir together the 2 tbsp gochujang, 1 tbsp gochugaru, 2 tbsp soy sauce, 1 tbsp rice syrup, 1 tbsp mirin, 1 tbsp sesame oil, 4 grated garlic cloves, 1 tsp grated ginger, and ½ tsp black pepper. Add the pork and sliced onion, mix until every piece is coated, and marinate covered in the refrigerator for 30 minutes. The sauce should cling rather than pool, so add no extra liquid. That thin slicing is what lets the pork cook through in minutes, while the onion softens and absorbs flavour in the marinade.

Separate the 4 bias-cut scallion pieces from the 2 thinly sliced scallions kept for the garnish, so the right ones go into the pan later. Set a large heavy skillet, sauté pan, or wok over medium-high to high heat and let it get properly hot before adding the 1 tbsp of neutral oil. The oil should shimmer and loosen across the surface within a few seconds. A wide base matters as much as the heat. That combination is what keeps the pork in contact with hot metal, so it chars lightly instead of steaming in its own juices.

Add the marinated pork and onion to the hot pan in a single layer if possible, or cook in 2 batches if the pan would otherwise be crowded. Stir-fry for 4–6 minutes, turning and tossing often, until the pork is cooked through with no raw pink left, the onion is tender, and the loose marinade has reduced to a thick, shiny glaze. Add the scallion pieces for the last 1–2 minutes and toss briefly, until some pork and onion edges catch a light char. Keep the heat high and the pan uncovered. That evaporation is what turns a wet red marinade into a clinging glaze rather than a soupy braise.

Taste and adjust if needed, and add a few drops of sesame oil off the heat if you want a little extra shine. Spoon a small mound of hot rice onto each of 4 plates or bowls, then arrange a generous portion of pork alongside it rather than fully over it. Scatter the 2 tsp of toasted sesame seeds and the thinly sliced scallions across the pork, and serve at once. The pork should look bright red, glossy, and lightly charred, not dark or wet. That immediate plating is what keeps the glaze glossy and the pork tender and juicy.