Begin by slicing the beef sirloin into thin strips, ensuring tenderness.

Chop the onion and bell peppers, setting them aside to maintain freshness.

In a mixing bowl, combine the sliced beef with soy sauce, sesame oil, minced garlic, and sugar. Toss well and let marinate for 15 minutes.

Heat a skillet over medium-high heat and add a splash of oil. Add the chopped onions and bell peppers, and sauté for about 5 minutes.

Push the sautéed veggies to one side of the skillet, and add the marinated beef. Cook for about 5 minutes, stirring occasionally.

Stir in the chopped kimchi and cook for an additional 2 minutes, allowing it to meld with the beef mixture.

Toast hoagie rolls under the broiler until lightly crisp. Scoop the beef and veggie mixture onto each roll, adding cheese on top.

Return the sandwiches to the broiler for 2 minutes until cheese melts, then serve and enjoy!