Slice the pork thin. For best results, chill the pork until firm, then slice across the grain into very thin pieces. Aim for 1/8–1/4 inch.
Make the marinade. In a large bowl, mix gochujang, gochugaru, soy sauce, sugar, rice vinegar, sesame oil, garlic, ginger, grated pear, black pepper, and sesame seeds until smooth.
Marinate the pork. Add pork, onion, green onions, and carrot. Toss well to coat.
Cover and refrigerate for at least 30 minutes, preferably 2–4 hours. Overnight gives the deepest flavor.
Preheat your pan or grill. Heat a large skillet or griddle over medium-high until hot. Add oil if your pan isn’t nonstick.
Cook in batches. Spread pork in a single layer.
Let it sear for 1–2 minutes before stirring. Cook 5–7 minutes total, until edges char slightly and the pork is cooked through. Avoid crowding to keep it from steaming.
Taste and adjust. If you want more heat, sprinkle in a pinch of gochugaru at the end.
If it needs brightness, add a splash of rice vinegar.
Garnish and serve. Finish with extra sesame seeds. Serve hot with rice or wrapped in lettuce with kimchi.