Start by slicing the chicken breast into even strips. In a bowl, add the cornflour, olive oil, and water to the chicken and mix well until all pieces are evenly coated. Let this sit while you prep the rest. Meanwhile, boil your chosen noodles according to the package directions, then drain and set aside.
Heat a wok or large non-stick pan over medium heat. Add about 2 tablespoons of olive oil. Once hot, add the marinated chicken strips. Sear and stir until golden brown and fully cooked, about 5–7 minutes. Once cooked, remove the chicken from the pan and set aside on a plate.
In the same pan, pour in 1 tablespoon of olive oil and reduce the heat to medium. Add the minced garlic and let it sizzle for about 10 seconds. Then toss in the sliced cabbage, carrots, red bell peppers, and onions. Stir frequently and let the veggies cook, covered, for 2 minutes to retain some crunch.
Return the cooked chicken to the pan with the vegetables. Add the noodles on top, gently loosening them with tongs or a spatula. In a small bowl, mix light soy sauce, dark soy sauce, sesame oil, salt, and chili flakes if using. Pour this sauce mixture over the noodles and chicken, and toss everything together to coat well. Let it all cook for another 2–3 minutes until well heated and combined.
Transfer the cooked lo mein to a serving dish. Sprinkle with sesame seeds and chopped spring onions if desired. Serve immediately while hot and flavorful. This dish pairs wonderfully with a side of pickled veggies or a light soup.