Heat a skillet on medium high with 1 tsp sesame oil and bring a medium pot of water to a boil. If using chicken breasts, slice each in half horizontally to create thin cutlets. Once the oil is hot, sear the sliced chicken breasts or boneless skinless chicken thighs until both sides are beautifully browned. Transfer to a plate.
Once the water comes to a boil, cook the rice noodles per package instructions, about 5 minutes. Once cooked, drain and rinse with cold water, then toss with 1/2 tsp sesame oil and set aside.
After the chicken has been removed from the pan, add 1 tsp sesame oil and fry the onion, celery, carrots and pepper. Slice the chicken breast and mix the sauce ingredients together.
Once the onion, pepper, carrots and celery have become soft, add the sauce and bring to a boil for a minute or two. Stir in the chicken, bok choy, bean sprouts and broccoli. Cover the pan with a lid and cook for a couple of minutes, until the broccoli is vibrant in colour. Stir in the rice noodles and serve hot!