Marinate the chicken: In a bowl, toss sliced chicken with 2 tablespoons soy sauce and 1 tablespoon cornstarch. Let sit 10 minutes while you prep the veggies and sauce.
Mix the sauce: Whisk soy sauce, oyster sauce, rice vinegar, honey, broth, cornstarch, sesame oil, and a pinch of red pepper flakes.
Set aside.
Preheat the pan: Heat a large skillet or wok over medium-high until hot. Add 1 tablespoon oil and swirl to coat.
Cook the chicken: Add chicken in a single layer. Sear 2–3 minutes, flip, and cook another 1–2 minutes until just cooked through.
Remove to a plate.
Stir-fry veggies: If the pan is dry, add a little more oil. Add broccoli, carrots, and onion. Stir-fry 2 minutes.
Add mushrooms and bell pepper; cook another 2–3 minutes until crisp-tender.
Add aromatics: Push veggies to the sides. Add garlic and ginger to the center; cook 20–30 seconds until fragrant.
Combine and sauce: Return chicken and any juices to the pan. Whisk the sauce again and pour it in.
Stir constantly 1–2 minutes until the sauce thickens and glazes everything.
Taste and finish: Adjust seasoning with more soy sauce, vinegar, or heat. Garnish with green onions and sesame seeds.
Serve: Spoon over hot rice or toss with noodles. Add a squeeze of lime if you like.