Slice the chicken breast into ~¼” thick slices against the grain. Place the sliced chicken in a non reactive bowl and dust with 1 tsp of baking soda, then toss the pieces well in the bowl and and dust with the other 1 tsp of baking soda and toss again. Add 1 Tbs of water to the bowl with the chicken and baking soda and toss well. Let sit for 15 minutes.

Rinse the baking soda off of the chicken with water and thoroughly pat dry the chicken so it will brown properly. (The baking soda "velvets" the meat to make it tender and gives it the unique texture). Season the chicken all over with salt and pepper.

While waiting on the chicken, mix together the chicken stock and cornstarch in a small bowl, then add in the mirin, soy sauce, oyster sauce, sesame oil and garlic and mix well. Note, oyster sauce may not fully incorporate, that's okay, it will in the pan.

Once the chicken is prepared, heat the oil in a large skillet over medium-high heat. Add the chicken and try to arrange it such that the pieces lay flat in the pan. Cook until golden on one side (2-3 minutes), then mix the chicken around in the pan and cook until cooked through (another ~90 seconds).

Reduce the heat to medium, push the chicken to the sides of the pan, and add the broccoli to the center. Stir fry for about one minute, then add the water chestnuts and stir fry for another minute. Add more oil to the pan if needed.

Next, lower the heat slightly, stir the sauce and add it to the pan. Cook and toss everything together until the sauce has thickened and evenly coats everything. Remove from heat and add in the chopped green onion, serve immediately over a bed of white or califlower rice.