Heat a large cast-iron skillet or wok over high heat.
Add 1 tablespoon oil until shimmering.
Add the chicken, season with salt and pepper, then reduce heat to medium.
Cook for about 4 minutes, stirring occasionally until fully cooked. Transfer to a plate.
Add the remaining oil.
Stir in broccolini, carrots, and bell peppers. Cook for 2 minutes.
Add mushrooms and bok choy. Cook another 3 minutes until crisp-tender.
Meanwhile, rinse the precooked yakisoba noodles under hot water to loosen them. Drain well.
In a small bowl, whisk together soy sauce, chicken stock, honey, brown sugar, ginger, garlic, and cornstarch until smooth.
Return the chicken to the skillet and add the noodles.
Pour the sauce over everything and toss continuously for 1–2 minutes until thickened and evenly coated.
Serve your 15 Minute Chicken Stir Fry immediately, garnished with green onions and sesame seeds.