Prepare the sauce: Add sauce ingredients in a small bowl or a pint mason jar. Mix until well combined and set aside.
Prepare your chicken: slice chicken diagonally against the grain into 1/2 inch thick pieces. Place the chicken into a medium-sized bowl, add salt, pepper, and cornstarch, and toss until well combined. Place in a large bowl and set aside.
Cook the chicken: Add 2 tablespoons of avocado or olive oil to your pan, add chicken pieces and fry until lightly golden. Best to do this in batches; you want to have space between your chicken pieces, so they don't steam but pan fry. Set cooked chicken aside. Wipe out the pan.
Cook frozen veggies: Add 1 tablespoon of cooking oil to your pan. Add the frozen veggies and cook until defrosted. Place in the same bowl as chicken and set aside. Wipe out the pan.
Cook ramen noodles: Add three cups of water to the pan and bring to a boil. Add noodles and let cook for 2-3 minutes. Helping separate the noodles as they cook. Cook to al dente. Drain and add to the same bowl with veggies and chicken. Set noodles aside.
Prepare dish: In the pan add the yakisoba sauce and cook for 30 seconds. Add all the cooked ingredients. Gently toss to combine. Top with scallions and toasted sesame seeds. Serve immediately.
Reheating: Add 1 tablespoon of water to noodles and heat in saute pan on medium-low until reheated.
Notes: Substitute oyster sauce with a vegan version. Substitute chicken with one block of the cubed tofu.