Begin by thinly slicing the beef sirloin into strips. Chop the onion and bell peppers into bite-sized pieces.

In a large bowl, combine soy sauce, sesame oil, minced garlic, and sugar. Add the beef sirloin, tossing gently to coat. Let marinate for at least 15 minutes.

Heat a tablespoon of vegetable oil in a large skillet over medium-high heat. Add the onions and bell peppers, sautéing for about 5 minutes until softened.

Push the sautéed vegetables to one side of the skillet and add the marinated beef in a single layer. Let sear for 2 minutes, then stir and cook until browned, about 5 minutes.

Stir in the chopped kimchi and cook for an additional 2 minutes, ensuring even distribution.

Take your toasted hoagie rolls and fill each with the beef and kimchi mixture. Top with cheese and broil for about 2 minutes until melted.

Serve immediately, ideally with sweet potato fries or cucumber salad.