How to Make It
In a small bowl, combine 1 tablespoon of the broth with the cornstarch. In a wok or a large nonstick frying pan, heat 1/2 tablespoon of the cooking oil over moderately high heat. Add the cashews; cook, stirring, until starting to char, 1 to 2 minutes. Transfer the nuts to a medium bowl and add a pinch of red-pepper flakes.
In the same pan, heat 1 tablespoon of the cooking oil over moderately high heat. Add the mushrooms and 1/4 teaspoon of the salt and cook, stirring occasionally, until golden brown, about 5 minutes. Transfer to the bowl with the cashews. Stir the scallion greens and sesame oil into the mushroom mixture.
Heat the remaining 1 1/2 tablespoons of cooking oil over moderately high heat. Add the scallion bulbs and garlic; cook, stirring, about 30 seconds. Add the broccoli and cook, stirring, for 1 minute. Add the cabbage; cook, stirring, until the cabbage wilts, about 2 minutes. Stir in the remaining 2 tablespoons broth and 1/4 teaspoon salt, 1/4 teaspoon red-pepper flakes, and the oyster and soy sauces. Stir the cornstarch mixture, add it to the pan, and bring to a boil. Cook, stirring, until the sauce coats the vegetables, about 1 minute. Serve topped with the mushroom mixture.