Stir-Fried Brussels Sprouts with Red Pepper

1 lb. small Brussels sprouts (3 cups)
2 Tbs. peanut oil
6 medium scallions, thinly sliced
1 Tbs. minced fresh ginger
1 medium clove garlic, minced
1/4 to 1/2 tsp. crushed red pepper flakes
1 medium red bell pepper, cored, seeded, and chopped
2 Tbs. lower-sodium soy sauce
2 Tbs. rice vinegar
Kosher salt

Trim any tough exterior leaves from the Brussels sprouts and halve each lengthwise. Slice each half lengthwise into thirds. Set aside.

Heat the oil in a large wok or 10-inch straight-sided skillet over medium-high heat. Add the scallions, ginger, garlic, and red pepper flakes and cook, stirring constantly, until fragrant, about 30 seconds. Add the Brussels sprouts and cook, stirring constantly, until they are bright green, about 4 minutes. Add the bell pepper, soy sauce, and vinegar. Cover the wok or skillet, reduce the heat to low, and simmer until the Brussels sprouts are crisp-tender, 6 to 8 minutes.

Uncover the wok or skillet, raise the heat to high, and bring the sauce to a full boil, stirring constantly, until reduced to a glaze, about 1 minute. Season to taste with salt and serve.