First, prepare the sauce. In a small bowl, combine soy sauce, brown sugar, sesame oil, rice vinegar, chili oil, oyster sauce, and powdered ginger. Whisk thoroughly until fully combined.
Preheat a wok over medium-high heat, then add the butter, swirling it around to help it melt.
Once the butter is fully melted, add minced garlic to the wok and cook until fragrant, about 1 to 2 minutes, moving it around to prevent sticking. If you hear a lot of sizzling right away, you may have to lower the heat so the garlic doesn't burn.
Pour the sauce into the wok and stir or swirl to incorporate the minced garlic and butter evenly with the sauce. Then add the udon and stir fry until steaming and noodles are warmed through, about 3 to 5 minutes.
Season with a pinch of salt and white pepper, tossing the noodles to combine. Then stir in sliced scallions and remove from heat. Serve immediately.