Cut the chicken breast into bite-sized pieces.
Slice the tomato and onion thinly.
Heat olive oil in a pan and stir-fry the chicken breast.
Once the chicken is cooked, add the tomato and onion and stir-fry together.
Boil the buckwheat noodles, then rinse in cold water.
In a bowl, place the noodles and the stir-fried chicken and vegetables.
Serve with Bun Cha sauce.