In a small bowl, mix together the soy sauce, oyster sauce, dark soy sauce, brown sugar, crushed red pepper, toasted sesame oil, chicken stock, and cornstarch. Set aside.

In a bowl, combine the beef strips, salt, cornstarch, and baking soda. Toss to coat, then set aside to marinate for 20-30 minutes.

Bring a pot of water to a boil and cook the udon noodles 1-2 minutes less than the package instructions. Drain the noodles and set them aside. Time this part with stir frying so you can add the noodles immediately to the wok. Otherwise add a teaspoon of oil to prevent them from sticking.

Heat the oil in a wok or large skillet over high heat. Once the oil is hot, add the marinated beef and stir-fry until browned and crispy. Remove the beef from the pan and set it aside.

In the same wok, in the remaining oil, add the ginger, garlic, and the white part of the spring onion, red chilies. Stir-fry for 1-2 minutes until fragrant. Add the bell pepper and carrots, and stir-fry for 2-3 minutes over high heat until the vegetables are slightly tender but still crisp.

Pour in the sauce and let it come to a simmer. Add the drained udon noodles to the wok with the fried beef. Toss everything together over medium-high heat for 2-3 minutes until well combined and heated through. Remove from heat and stir in the green part of the spring onion.