Boil noodles according to package directions.
Drain and toss lightly with oil to prevent sticking. Set aside.
In a small bowl, whisk together gochujang, soy sauce, gochugaru, brown sugar, rice vinegar, sesame oil, and water.
Heat oil in a large wok or skillet over medium-high heat.
Add garlic and ginger; stir 20–30 seconds until fragrant.
Add onion and mushrooms; cook 2–3 minutes until softened.
Add bell peppers, cabbage, and carrots; stir-fry 2 minutes.
If using protein, add now and cook until done.
Add cooked noodles to the pan.
Pour in sauce and toss well to coat.
Stir-fry 2–3 minutes until glossy and slightly caramelized.
Toss in green onions and serve.
