Combine the beef and soy sauce in a medium bowl; cover with plastic wrap and refrigerate at least 10 minutes or up to 1 hour, stirring once. Meanwhile, whisk the sherry, chicken broth, oyster sauce, sugar, sesame oil, and cornstarch in a measuring cup. Combine the garlic, ginger and 1 1/2 teaspoons peanut oil in small bowl.
Drain the beef and disgard the liquid. Heat 1 1/2 teaspoons peanut oil in a 12-inch nonstick skillet over high heat until smoking. Add half of the beef to the skillet and break up clumps; cook without stirring, 1 minute, then stire and cook until beef is browned about the edges, about 30 seconds. Transfer the beef to a medium bowl. Addd 1 1/2 teaspoons peanut oil to the skillet, heat until just smoking, and repeat with the remaining beef.
Add 1 tablespoons peanut oil to the now-empty skillet; heat until just smoking. Add the broccoli and cook 30 seconds; add the water, cover the pan, and lower heat to medium. Steam the broccoli until tender-crisp, about 2 minutes; transfer to a paper towel-lined plate. Add the remaining 1 1/2 teaspoons peanut oil to the skillet; increase the heat to high and heat until just smoking. Add the bell pepper and cook, stirring frequently, until spotty brown, about 1 1/2 minutes. Clear the center of the skillet; add the garlic and ginger to the clearing and cook, mashing the mixture with a spoon, until fragrant, about 15 to 20 seconds, then sture the mixture unto the peppers. Return the beef and broccoli to the skillet and toss to combine. Whisk the sauce to recombine, then add to the skillet; cook, stirring constantly, until the sauce is thickened and evenly distributed, about 30 seconds. Transfer to a serving platter, sprinkle with the scallions, and serve.