Arrange a rack in the middle of the oven and preheat to 450F. Place cauliflower on baking sheet, drizzle with 2 Tbsp. of the oil and season with salt and pepper. Spread into an even layer and roast until crisp and golden, stirring halfway through about 20-25 minutes.
Heat the remaining 2 Tbsp oil in a wok over medium-high heat until shimmering. Add the ginger and stir until caramelized, 1-2 minutes. Add the onion and garlic, and cook for 2 minutes more, making sure they don't burn.
Turn up the heat to high, then add the roasted cauliflower and scallions. Stir-fry for 30 seconds. Add the rice wine, soy sauce, sesame oil, red pepper flakes, and sugar. Stir-fry for about 1 minute, then serve with rice if desired. Enjoy!