Step 1

Spread the flank steak out flat, cover with plastic wrap, and place in the freezer until partially frozen, 20 to 30 minutes.

Step 2

Remove beef from the freezer and slice across the grain into very thin slices.

Step 3

Whisk the chicken stock and cornstarch in a freezer-safe bowl until smooth; whisk in the hot chili oil, hoisin sauce, oyster sauce, sherry, sugar, soy sauce, and crushed red pepper flakes. Place the beef into the sauce, stir to coat well. Cover and freeze until frozen, about 1 hour.

Step 4

Remove from the freezer and allow to defrost, about 30 minutes.

Step 5

Heat a wok over high heat until very hot, and pour in the peanut oil. Immediately add garlic, cook and stir in the hot oil until fragrant, about 15 seconds. Mix in the Swiss chard and green onions; cook and stir the vegetables until they turn bright green, about 3 minutes, and then remove from the wok.

Step 6

Pour the defrosted beef mixture into the hot wok; cook and stir until the meat browns and the sauce forms a glaze, 3 to 5 minutes. Return the cooked vegetables to the wok, sprinkle with salt and pepper, mix to combine well; serve hot.