Prepare the marinade by mixing soy sauce, brown sugar, sesame oil, garlic, ginger, and black pepper in a bowl.

Add the thinly sliced beef to the marinade and let it sit for at least 30 minutes, or up to overnight in the refrigerator.

While the beef marinates, cook your rice according to package instructions and prepare your vegetables by slicing them into thin strips.

Heat a skillet or grill pan over medium-high heat. Once hot, add the marinated beef and cook until browned and cooked through, about 5-7 minutes.

Add the mixed vegetables to the skillet and stir-fry with the beef for an additional 3-4 minutes until they are tender but still vibrant.

In a separate bowl, combine gochujang and mayonnaise to create the creamy sauce. Whisk until smooth and well blended.

To assemble the bowls, place a serving of rice in each bowl, top with the beef and vegetable mixture, and drizzle with creamy gochujang sauce.

Garnish the bowls with chopped green onions and sesame seeds before serving.