01 - In a shallow dish, rub the steak with olive oil, Worcestershire sauce, salt, and pepper. Let marinate for 10 minutes at room temperature.
02 - Heat a skillet over medium heat. Add butter, then sauté onions (and bell pepper, if using) until soft and caramelized, about 8–10 minutes. Transfer to a plate.
03 - Increase skillet heat to high. Sear the steak for 2–3 minutes per side for medium-rare, or to desired doneness. Rest steak on a cutting board for 5 minutes, then slice thinly against the grain.
04 - While steak rests, slice the rolls open and toast lightly.
05 - Mix mayonnaise and Dijon mustard; spread inside the rolls.
06 - Layer arugula, tomato slices, caramelized onions, and bell peppers onto the bottom halves.
07 - Top with sliced steak and cheese. If desired, place under a broiler for 1–2 minutes to melt the cheese.
08 - Close sandwiches, slice in half, and serve immediately.