Whisk soy sauce, honey, brown sugar, vinegar, garlic, ginger, red pepper flakes, and sesame oil in a bowl.
Pat chicken dry and season lightly with black pepper.
Heat oil in a large skillet over medium-high heat.
Sear chicken until browned on both sides, about 4–5 minutes per side.
Pour in the sauce and simmer, stirring, until slightly thick and glossy, 6–8 minutes.
Stir cornstarch with water. Add slurry to skillet and cook until sticky and shiny, 1–2 minutes.
Rest 5 minutes. Scatter green onions and sesame seeds. Serve hot over rice.