Marinate the chicken: Toss chicken with soy sauce, cornstarch, and black pepper. Let it rest for 10 minutes.
Cook the chicken: Heat oil in a wok, stir-fry the chicken until golden, then set aside.
Stir-fry the veggies: Add oil, then sauté cabbage, carrots, and bell peppers until slightly softened.
Prepare the sauce: Mix soy sauce, oyster sauce, sesame oil, sugar, garlic, ginger, sriracha, and chili flakes.
Combine everything: Return chicken to the wok, add noodles, and pour in the sauce.
Thicken it up: Stir in the cornstarch slurry and toss until fully coated.
Garnish and serve: Sprinkle with green onions and enjoy immediately.