Cut the steak lengthwise (with the grain) into several long strips about 2 inches wide. Holding your knife at a sharp angle to the board, cut each strip crosswise (against the grain) into ⅛ inch slices. In a large bowl, whisk together ½ cup of the soy sauce, 2 Tbs of the sherry, the brown sugar, and the cornstarch. Add the beef and toss to coat each slice.
In a small bowl, combine the scallions, garlic, and ginger and set aside. In another small bowl, combine the chicken broth, vinegar, sugar, the remaining 2 Tbs soy sauce, and 1 Tbs sherry, and set aside.
In a saute pan or wok over medium-high heat, heat 2 Tbs of the olive oil. When the oil is hot enough to sizzle a scallion ring, add half of the beef and cook, tossing often, until it's slightly firm to the touch and has no traces of pink, 3 minutes. Using a slotted spoon, transfer the beef to a large plate.
Cook the remaining beef in the same way and reserve with the first batch. Add the remaining 1 Tbs olive oil and the scallion mixture to the pan and cook, stirring, until the mixture is fragrant but not browned 20-30 seconds.
Stir the chicken broth mixture and add it to the pan, Raise the heat to high, scrape the pan with a wooden spoon, and cook for 2 minutes. Reduce the heat to medium, add the snow peas, and cook until they're crisp-tender, about 3 minutes. Return the beef to the pan and stir in the orange zest. Toss to heat through and serve.