Combine beef and soy sauce in medium bowl; cover with plastic wrap and refrigerate at least 10 minutes or up to 1 hour, stirring once.

Meanwhile, whisk sherry, chicken broth, oyster sauce, brown sugar, sesame oil, and cornstarch in measuring cup.

Combine garlic, ginger, and 1 ½ teaspoons peanut oil in small bowl.

Drain beef and discard liquid.

Heat 1 ½ teaspoons peanut oil in 12-inch nonstick skillet over high heat until smoking.

Add half of beef to skillet and break up clumps; cook, without stirring, for 1 minute, then stir and cook until beef is browned around edges, about 30 seconds.

Transfer beef to medium bowl.

Heat 1 ½ teaspoons peanut oil in skillet, and repeat with remaining beef.

Add 1 tablespoon peanut oil to now-empty skillet; heat until just smoking.

Add broccoli and cook 30 seconds; add water, cover pan, and lower heat to medium.

Steam broccoli until tender-crisp, about 2 minutes; transfer to paper towel–lined plate.

Add remaining 1 ½ teaspoons peanut oil to skillet; increase heat to high and heat until just smoking.

Add bell pepper and cook, stirring frequently, until spotty brown, about 1 ½ minutes.

Clear center of skillet; add garlic and ginger to clearing and cook, mashing mixture with spoon, until fragrant, 15 to 20 seconds, then stir mixture into peppers.

Return beef and broccoli to skillet and toss to combine.

Whisk sauce to recombine, then add to skillet; cook, stirring constantly, until sauce is thickened and evenly distributed, about 30 seconds.

Transfer to serving platter, sprinkle with scallions, and serve.