Add the thinly sliced pork butt, chopped yellow onion, and 0.5 cup chopped scallions in a large bowl. Set aside.

Make the marinade in a small mixing bowl by whisking together the soy sauce, grated apple, seasoned rice wine vinegar, Gochujang Korean chili paste, light brown sugar, minced garlic, grated ginger, and sesame oil.

Pour the marinade into the bowl of the pork and onions. Stir to fully coat all the pork with the marinade.

Cover the bowl with plastic wrap and refrigerate for 1 hour or up to overnight to allow the pork to marinate and absorb the flavors.

Add the peanut oil to a large, heavy-duty skillet on high heat. Once the oil is very hot, add half the marinated pork. Cook for 4-6 minutes. Remove the cooked pork to a serving plate and set aside.

Add the remaining marinated pork to the skillet (add an additional 1 tablespoon of peanut oil if needed) and cook for another 4-6 minutes or until the pork is cooked through and the marinade thickens into a glaze.

Add the second batch of cooked Korean BBQ pork to the serving plate and garnish with the remaining 0.25 cup of chopped scallions and optional sesame seeds.