Mix soy sauce, vinegar, sugar, cornstarch, salt, and 2 tbsp water into a bowl.
Heat oil in a wok, stir-fry peanuts until light golden; remove and set aside.
In the same wok, sauté dry red chilies, ginger paste, and garlic paste for 1 minute.
Add halved button mushrooms and stir-fry on high flame for 3 minutes.
Pour in sauce mixture, stir until glossy and thickened, then toss with peanuts and chopped spring onions.