Slice the chicken breast into ~¼” thick slices. Arrange the sliced chicken on a cutting board or plate so it’s laying flat. Dust with ~1 teaspoon of baking soda, then flip all the pieces and dust with the other ~1 teaspoon of baking soda. Let sit for 15 minutes. After 15 minutes, rinse the baking soda off of the chicken with water then thoroughly pat dry. Season the chicken all over with salt and pepper.
Make the Stir Fry:
Bring a large pot of water to a boil for the udon. Once boiling, cook per package directions, then drain and set aside until needed.
Meanwhile, mix together the chicken stock and cornstarch in a small bowl, then add in the other sauce ingredients and mix well. The oyster sauce may not fully incorporate, that's okay, it will in the pan.
Once the chicken is prepared, heat a generous swirl of oil in a large skillet or wok 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).
Remove the chicken to a plate. Add a little more oil to the pan if needed and reduce the heat to medium, then add the onion and cook until it turns translucent and a little golden, about 3-4 minutes.
Next, add the garlic and the white portions of the green onion. Cook for about a minute, then add the carrots and cook for another minute, then add the baby bok choy.
Cook this together for 1-2 minutes then add the noodles, chicken and sauce.
Cook everything together until the sauce has thickened and coated everything, another 1-2 minutes. Top with the green portion of the green onions and serve immediately.
Notes
If you can't find frozen udon, or just want to use something else, this recipe should work well with 6 ounces of dried pasta or noodles per batch!