Prep the steak: Freeze for 15 min, then slice it paper-thin across the grain.
Cook veggies: In a large skillet, heat 1 tbsp oil. Sauté onion and pepper over medium heat until soft and slightly browned (about 6–8 min). Set aside.
Cook steak: Add 1 tbsp oil to the pan. Cook steak in batches on high heat. Season with salt, pepper, and garlic powder. Cook for 2–3 min until browned.
Combine: Add veggies back in. Mix well with the steak. Lay cheese slices over the top. Cover for 1–2 min to melt.
Assemble: Split and lightly toast the hoagie rolls. Fill with hot steak, veggies, and melted cheese.