Heat vegetable oil in a large skillet over medium-high heat. Add the chicken thighs skin-side down and sear for 4–5 minutes until golden brown. Flip and transfer to a plate.

Reduce the heat to medium, add sliced onion, minced garlic, and grated ginger to the same skillet. Sauté for about 2 minutes until onions become translucent.

Sprinkle brown sugar over the seared chicken thighs and stir to coat evenly. Let cook for about 3 minutes until the sugar melts and caramelizes.

Pour in regular soy sauce, dark soy sauce, and chicken broth. Bring to a gentle simmer for another 1-2 minutes.

Lower the heat, cover, and let simmer for about 10 minutes for flavors to meld. Add chili flakes for heat if desired.

Stir in sesame oil, taste and adjust seasoning if necessary. Serve over fluffy rice garnished with chopped green onions.