Place the flank steak in a large plastic zip-top bag. To make marinade, combine soy sauce, sugar, garlic, chili garlic sauce, cilantro and lime juice in a bowl and mix well. Pour over steak, seal tightly and lay flat in freezer for 20 minutes.
In the meantime, combine mayo, sesame oil and cayenne pepper and mix well. Place in refrigerator until ready to use.
Place sesame seeds in a dry pan over medium heat and toast until fragrant and slightly brown; set aside. Vegetable toppings may, also, be prepared while marinating.
After 20 minutes, remove beef from freezer. Slice against grain on a diagonal into thin strips. Place beef back in marinade and let sit for 20 more minutes. (Note: the recipe does not call for salt, but I do lightly salt.).
Remove meat from marinade. Heat an indoor grill pan or heavy skillet on medium-high heat until very hot. Brush with vegetable oil. Place beef strips on pan at least 2 inches apart; do not overcrowd. Sear meat in batches, 30 seconds per side.
Toast rolls lightly and divide spicy mayo evenly among them, spreading on the top and bottom halves. Distribute beef along with cucumber, bell pepper, green onions, carrots, arugula or other leafy greens, sesame seeds and jalapenos among the sandwiches. Slice each sandwich in half before serving.