In a bowl, combine the sliced flank steak, soy sauce, rice wine, cornstarch, and a pinch of salt and pepper. Mix well and let marinate for at least 15 minutes.

Heat the vegetable oil in a large skillet over medium-high heat. Add the marinated beef and cook for about 3-4 minutes until browned and cooked through. Remove from heat and set aside.

In the same skillet, briefly sauté the scallions for about 1-2 minutes until they are slightly wilted. Remove from heat.

To assemble, lay a tortilla or scallion pancake flat on a clean surface. Place a portion of the cooked beef, sautéed scallions, and julienned cucumber in the center. Drizzle with sesame oil.

Roll the tortilla tightly around the filling, folding in the sides as you go to secure the filling inside. Repeat with the remaining tortillas and filling.

Slice each roll into bite-sized pieces and serve warm or at room temperature.