Cut chicken into thin strips or slices. Season the chicken with soy sauce and mirin. Mix it well and set it aside.
Blanch the udon in the hot boiling water for 1-2 minutes, strain it, rinse with cold water. Set it aside. ( Or you can prepare by the packet instructions. )
Heat pan over medium high-heat drizzle 1 tbsp of oil and add marinated chicken. Stir fry for 2-3 minutes or until the chicken is cooked through.
Next, add the mushroom, onion, carrot, cabbage, and chilli pepper. Stir fry for another 1-2 minutes.
Place the udon noodles in the pan. Pour the sauce mix over the noodles and combine well with the rest of the ingredients. Cook until the sauce is absorbed and the noodles are cooked through.
Finish with spring onions and make a final quick toss. Transfer to a serving plate and serve immediately.