Meanwhile, slice steak 1/4-inch thick, then cut slices crosswise in half. Whisk 1 T. peanut oil, the sherry, soy sauce, honey, cornstarch, and half the ginger and garlic in small bowl. Add steak and toss to combine.
Heat 1 T. peanut oil in large heavy skillet over high heat until a drop of water evaporates on contact. Add remaining ginger, garlic, and the scallions. Reduce heat to medium-high; stir-fry 1 minute. Transfer with slotted spoon to medium bowl. Add peas, squash and bell pepper to skillet; stir-fry until crisp-tender, 3-4 minutes. Add to scallions.
Add 1 T. oil to skillet and heat over high heat. Add pepper flakes to steak and stir to separate pieces;. Add steak to skillet; stir-fry until tender, about 3 minutes. Return vegetables to skillet; stir-fry until hot, about 1 minute.