Freeze the beef chuck roast for 40 minutes to 2 hours to make slicing easier.

In a large mixing bowl, combine granulated sugar, apple cider vinegar, Korean BBQ sauce, soy sauce, water, crushed garlic, and black pepper. Stir until the sugar dissolves.

Add the sliced beef to the marinade, ensuring all pieces are coated. Seal in the refrigerator for at least 24 hours.

Preheat a large skillet over high heat for about 2 minutes, add a splash of sesame oil.

Cook the marinated beef in batches for about 5 minutes each, stirring until browned.

Remove from heat and serve hot, paired with rice, vegetables, and garnishes like onions or sesame seeds.