Bring a large pot of salted water to a boil.
Trim florets from cauliflower. Cut white part of green onions diagonally into 1-inch pieces. Thinly slice the green part, and set aside.
Set up a large bowl of ice water. Add cauliflower to boiling water, and cook 2 minutes. Drain, and transfer cauliflower to ice water. When the cauliflower is cool enough to handle, drain, and pat it dry.
Whisk together soy sauce, brown sugar, sesame oil, mirin, cornstarch, chili garlic sauce, ginger, garlic, sherry, vinegar and red pepper flakes, and set aside.
Heat a wok or large sauté pan over high heat. Add oil, swirling the pan to coat. Add cauliflower and white part of the green onions. Stir-fry 2-3 minutes, or until crisp-tender. Add sauce and peanuts, tossing to coat, and cook 1 minute, or until thickened. Transfer to a platter, and garnish with sliced green onions.