In a bowl, combine chicken strips with baking soda, MSG, black pepper, soy sauces, and cornflour. Mix well and let marinate for 15 minutes.
In another bowl, whisk together soy sauces, sriracha, oyster sauce, rice vinegar, sesame oil, water, sugar, white pepper, MSG, chicken powder, black pepper, and cornflour. Set aside.
If using vacuum-packed cooked udon, soak them in boiled water for 4–5 minutes until loosened. Drain and set aside.
Alternatively, you can use other noodles like chow mein or linguine. Cook them according to package instructions.
Heat oil in a large pan or wok over medium-high heat. Add the marinated chicken and cook for 3–4 minutes until it starts to turn golden.
Without removing the chicken, add garlic and onions directly into the pan. Sauté for about 1 minute.
Add sliced bell peppers and stir-fry with the chicken for 1–2 minutes.
Add the soaked udon noodles and pour in the prepared sauce. Toss everything together on high heat until the noodles are evenly coated and the sauce thickens slightly.
Garnish with sesame seeds and serve hot.
Notes
Note on Noodles: I used cooked udon noodles that just needed soaking in boiled water for 4–5 minutes. You can substitute with chow mein noodles, ramen, or even linguine, just cook according to package instructions.