Drizzle oil in a pan and add diced onions. Cook for 2–3 minutes, or until the vegetables start to soften.
Sprinkle with a little salt.
Add the bell peppers and cook another 3–4 minutes.
Stir in chopped kimchi and cook for 1 more minute.
Remove the vegetables from the pan and set them aside.
In the same pan, add the beef and cook until browned.
Season with garlic powder, salt, soy sauce, and a splash of kimchi juice.
Return the cooked onions and bell peppers to the pan and mix everything together.
Lay provolone slices over the beef and veggie mixture.
Cover the pan and let the cheese melt for 1–2 minutes.
In a separate pan, melt a little butter.
Lay the hoagie rolls cut-side down and toast on low heat until golden and slightly crispy.
Fill each hoagie roll with the cheesy beef and veggie mixture.
Top with kimchi.
Enjoy!