In a mixing bowl, combine finely chopped lemongrass, minced garlic, grated ginger, fish sauce, sugar, and vegetable oil. Stir well until the mixture is smooth and all ingredients are evenly blended.

Add the chicken to the marinade, ensuring each piece is well coated in the mixture. Cover the bowl with plastic wrap and refrigerate for at least 30 minutes.

Before cooking, preheat your grill or a non-stick skillet over medium-high heat.

Carefully place the marinated chicken on the grill or in the hot skillet. Sear each side for about 6-8 minutes, until the chicken is opaque and browned.

Check the internal temperature of the chicken with a meat thermometer. It should reach 165°F.

Once cooked, remove the chicken from the heat and let it rest for about 5 minutes before slicing and serving.