In a large bowl, combine the chicken thighs with fish sauce, soy sauce, and rice vinegar. Mix well to ensure the chicken is fully coated in the marinade. Let sit for at least 30 minutes or refrigerate overnight.

In a medium saucepan, add sugar and water, stir gently, and bring to a boil over medium heat. Cook undisturbed for about 5-7 minutes until golden amber.

Carefully pour in vegetable oil into the caramel, stir in minced garlic and grated ginger. Sauté for 1-2 minutes until fragrant.

Add the marinated chicken thighs to the skillet, sear them over medium-high heat for about 5-7 minutes until browned and caramelized.

Pour the caramel sauce over the browned chicken, cover and simmer on low for 15-20 minutes until the chicken is cooked through.

In the last 5 minutes, stir in oyster sauce and sliced red chilies. Adjust seasoning if needed.

Garnish with freshly chopped cilantro and serve hot over steamed jasmine rice.