Make the marinade: In a bowl, whisk soy sauce, honey, rice vinegar, garlic, ginger, sesame oil, and red pepper flakes or sriracha if using.
Marinate the chicken: Add chicken and coat well.
Cover and refrigerate for at least 30 minutes, up to 8 hours. The longer it sits, the deeper the flavor.
Prepare the sauce slurry: In a small cup, mix cornstarch with 2 tablespoons of water until smooth. Set aside.
Heat the pan: Set a large skillet over medium-high heat and add the neutral oil.
Let it get hot but not smoking.
Sear the chicken: Lift pieces from the marinade, letting excess drip back into the bowl. Sear in batches for 2 to 3 minutes per side until golden. Don’t overcrowd the pan.
Build the sauce: Reduce heat to medium.
Pour remaining marinade into the pan and bring to a simmer for 1 to 2 minutes.
Thicken: Stir in the cornstarch slurry and cook 1 to 2 minutes, stirring, until the sauce turns glossy and coats the chicken.
Taste and adjust: Add a splash more vinegar for brightness or a drizzle of honey for extra sweetness if needed.
Finish and garnish: Turn off the heat. Sprinkle with green onions and sesame seeds.
Serve: Spoon over rice or noodles, or pair with steamed broccoli or a crisp cucumber salad.