Slice the onion thinly and soak in cold water to remove the pungency, then drain well. Wash the wild chives thoroughly and cut them into bite-size pieces. If the bulb part of the wild chive is too large, gently press it with the back of a knife.
Boil the chicken breast for 12 minutes, then immediately transfer to cold water to cool slightly. Shred the chicken breast into thin pieces.
Mix rice vinegar, soy sauce, anchovy sauce, and sesame oil to make the dressing.
Add the onion, wild chives, chicken breast, and dressing together, and toss lightly to combine. Enjoy!