In a bowl, combine the soy sauce, oyster sauce, sesame oil, black pepper, and sugar. Add the sliced beef and marinate for at least 30 minutes.
Heat a large skillet over medium-high heat and add the vegetable oil. Once hot, add the marinated beef in a single layer. Cook for about 2-3 minutes on each side until browned and cooked through. Remove from heat.
Lay a tortilla or pancake flat on a clean surface. Place a few pieces of cooked beef, a couple of scallion pieces, and some julienned cucumber on one end of the tortilla. Roll it tightly, starting from the filled end.
Repeat with the remaining tortillas and filling.
Slice each roll into bite-sized pieces and serve warm.