Prep the chicken: Pat the chicken thighs dry with paper towels and trim excess fat.
Cut into large bite-size pieces or leave whole if you prefer. Season lightly with pepper (skip salt for now since soy sauce is salty).
Make the sauce base: In a bowl, whisk soy sauce, brown sugar, honey, rice vinegar, mirin (if using), minced garlic, grated ginger, and 1/2 cup water. Set aside.
Heat the pan: Place a large skillet over medium-high heat.
Add 1 tablespoon oil. When the oil shimmers, add half the chicken in a single layer. Don’t crowd the pan.
Brown the chicken: Sear 3–4 minutes per side until nicely browned.
Transfer to a plate and repeat with remaining chicken, adding more oil if needed.
Deglaze and add sauce: Lower heat to medium. Pour the sauce into the pan, scraping up browned bits with a spatula. Return all chicken to the skillet and simmer 4–6 minutes, stirring occasionally.
Thicken the sauce: Stir cornstarch with 1 tablespoon water to make a slurry.
Drizzle into the simmering sauce while stirring. Cook 1–2 more minutes until the sauce turns glossy and coats the chicken. Add sesame oil for aroma.
Taste and adjust: For more sweetness, add a splash of honey.
For more tang, add a bit more vinegar. If too salty, add a tablespoon or two of water and simmer briefly.
Garnish and serve: Sprinkle with sesame seeds and scallions. Serve hot over rice with your favorite vegetables.
Spoon extra sauce over everything.