Preheat your grill or skillet over medium-high heat.
Rub the flank steak with olive oil, salt, and pepper.
Grill the steak for 6-8 minutes on each side for medium-rare.
Remove the steak from heat and let it rest for 5 minutes.
Slice the sandwich rolls in half.
Place cheese on the steak during the last minute of grilling to melt.
Slice the steak against the grain into thin strips.
Layer arugula or lettuce on the bottom half of each roll.
Add the sliced steak on top of the greens.
Top with tomato slices and any additional toppings, then close the sandwich.