Combine all sauce ingredients and set aside.
Heat the oil in a large frying pan over high heat and add the sliced onion and minced garlic. Cook until they begin to turn golden, about 1 1/2 minutes.
Add the chicken pieces and cook until the exterior is mostly white and no longer pink.
Pour in the prepared sauce and continue cooking for another minute until the chicken develops a caramelised colour.
Add the carrot sticks and sliced capsicum, stir and cook together for 1 minute to soften the vegetables.
Push the chicken and vegetables to one side of the pan, then pour in the water and add the noodles.
Once the water starts simmering around the edges, let the noodles cook for 45 seconds before flipping them over.
Cook for an additional 30 seconds, then separate the noodles and mix everything together well.
Add the sliced cabbage and stir everything for 1 more minute until the sauce thickens and coats the noodles evenly, and the noodles are fully cooked.
Serve immediately, topped with the green onion or shallots if desired.