Remove chicken thighs from the fridge and let sit at room temperature for 15 minutes. Pat each piece dry with paper towels.

In a mixing bowl, whisk together the soy sauce, brown sugar, minced garlic, grated ginger, rice vinegar, sesame oil, water, and black pepper until the sugar is dissolved.

Heat a skillet over medium-high heat and add neutral cooking oil. Once hot, sear chicken thighs skin-side down for 4-5 minutes until golden brown, then flip and cook for another 4-5 minutes.

Add the prepared sauce into the skillet, scraping up any browned bits. Bring to a gentle simmer over medium heat for 5-7 minutes.

Return chicken thighs to the skillet, skin-side up. Cover and lower heat to medium-low, simmer for 20-25 minutes until internal temperature reaches 165°F (75°C).

In a small bowl, combine cornstarch with 2 tablespoons of water to create a slurry. Stir into the sauce in the skillet and cook for 2-3 minutes until thickened.

Remove from heat and sprinkle sliced green onions and sesame seeds over the chicken before serving.