Place the chuck roast in a 6-8 quart slow cooker. Whisk together the soy sauce, brown sugar, gochujang, rice vinegar, sesame oil, garlic, ginger, beef broth, applesauce, fish sauce and black pepper, then pour over the beef.
Cover and cook on LOW for 8-9 hours or HIGH for 5-6 hours, until the beef shreds effortlessly with a fork.
Transfer the beef to a bowl and shred with two forks (or shred right in the slow cooker), then return it to the pot.
Whisk the cornstarch and cold water together, stir into the slow cooker and cook on HIGH for 10-15 minutes, until the sauce thickens slightly and coats the beef.
Divide rice among bowls and top with the shredded Korean beef, cucumbers, green onions, sesame seeds and any other toppings. Drizzle extra sauce over everything before serving.
Slow-cooker recipe by Tawnie Graham (@krolls_korner): krollskorner.com/recipes/dinner/slow-cooker-korean-inspired-beef-bowls/