In a mixing bowl, combine the soy sauce, sesame oil, minced garlic, minced ginger, salt, and pepper. Add the thinly sliced beef and marinate for at least 15 minutes to enhance the flavor.
Take a slice of marinated beef and place a small handful of enoki mushrooms at one end. Roll the beef around the mushrooms tightly and secure with a toothpick if necessary. Repeat with the remaining beef and mushrooms.
Heat the vegetable oil in a large skillet over medium-high heat. Once hot, add the beef rolls to the skillet, seam side down. Cook for about 3-4 minutes on each side, or until the beef is browned and cooked through.
Remove the beef rolls from the skillet and let them rest for a minute. Remove any toothpicks if used.
Slice the rolls into bite-sized pieces and arrange them on a serving platter. Garnish with sliced green onions before serving.