Start by preparing the sauce. In a small bowl, combine 2 tablespoons of soy sauce, 1 tablespoon of white vinegar, 2 tablespoons of sugar, 1 teaspoon of cornstarch, and 1 teaspoon of red chili flakes. Mix until the sugar and cornstarch are dissolved. Set aside.

Slice 500 grams of chicken breast into thin strips. In another bowl, toss the chicken with a pinch of salt and 1 teaspoon of cornstarch.

Cook 200 grams of egg noodles according to package instructions, usually by boiling in water for about 5-6 minutes. Drain and set aside.

Heat 1 tablespoon of sesame oil in a large skillet or wok over medium-high heat. Add the chicken and stir-fry until it starts to brown and is nearly cooked through, about 5-6 minutes. Remove the chicken from the skillet and set aside.

In the same skillet, add another tablespoon of sesame oil. Add 1 sliced bell pepper, 1 sliced onion, 2 minced garlic cloves, and 1 tablespoon of grated ginger. Stir-fry the vegetables until they are just tender, about 3-4 minutes.

Return the chicken to the skillet along with the cooked noodles and the prepared sauce. Toss everything together and cook for an additional 2-3 minutes, until the sauce has thickened and everything is heated through.

Serve hot, garnished with chopped spring onions and additional red chili flakes if desired.