To make slicing easier, freeze for 30 minutes to 1 hour:
Meanwhile, trim and cut into 2-inch lengths, then divide into 15 bundles (2 or 3 pieces each):
Cut the beef into 15 very thin slices. Place each slice between 2 sheets of plastic wrap and pound lightly to an even thickness with a mallet or the bottom of a small skillet. Roll a piece of beef snugly around each green onion bundle, wrapping it 2 to 3 times, and secure with a toothpick.
Heat in a large skillet over high heat:
Add the rolls seam side down and sear. Once the seams have sealed, turn to brown the rolls on all sides. After about 2 minutes, when the beef has changed color, whisk together and add:
Reduce the heat slightly and cook for 1 minute, shaking the skillet to keep the rolls from sticking. Transfer the rolls to a plate and let cool slightly, then remove the toothpicks. If there is a lot of sauce left in the skillet, reduce over high heat to 2 tablespoons. Just before serving, return the rolls to the skillet over high heat and shake to glaze them with the sauce. Slice each roll crosswise in half and serve warm.