In a bowl, combine soy sauce, sesame oil, brown sugar, minced garlic, minced ginger, and black pepper. Add the flank steak and marinate for at least 30 minutes, or up to 2 hours in the refrigerator for more flavor.

Preheat a grill or skillet over medium-high heat. Remove the steak from the marinade and cook for about 4-5 minutes on each side, or until it reaches your desired level of doneness. Let the steak rest for 5 minutes before slicing it thinly against the grain.

While the steak is resting, prepare the garlic mayo by mixing mayonnaise, sriracha, and lime juice in a small bowl. Adjust the sriracha to your preferred spice level.

Slice the hoagie rolls open and spread a generous amount of garlic mayo on each side.

Layer the shredded lettuce, sliced cucumber, julienned carrot, and sliced steak on the rolls. Top with jalapeño slices if desired.

Close the sandwiches and serve immediately, or wrap them in foil to keep warm until ready to eat.