Start by cutting the beef chuck roast into 1-inch pieces. This helps the meat cook evenly and absorb the marinade flavors.

In a mixing bowl, combine soy sauce, brown sugar, rice vinegar, sesame oil, minced garlic, ginger, black pepper, and red pepper flakes.

Add the beef pieces to the bowl with the marinade. Stir well to ensure every piece is coated.

Pour the beef and marinade mixture into the slow cooker.

Cover and set the slow cooker to low for 6-8 hours or high for 3-4 hours.

After the cooking time, check if the beef is fork-tender.

Once done, transfer the beef to a serving platter and sprinkle with sliced green onions and sesame seeds.

Serve the beef over rice, noodles, or in lettuce wraps.

For an extra burst of flavor, let the beef marinate in the fridge overnight before slow cooking.