Prepare the Marinade: In a mixing bowl, whisk together the lime juice, vegetable oil, soy sauce, fish sauce, brown sugar, minced garlic, grated ginger, and red chili flakes. Make sure the sugar dissolves completely to create a smooth marinade.
Marinate the Chicken: Put the chicken thighs in a resealable bag or a shallow bowl. Pour the marinade over the chicken, making sure all pieces are evenly coated. Seal the bag or cover the bowl, then refrigerate for a minimum of 30 minutes, or up to 2 hours for deeper flavor absorption.
Preheat the Grill: While the chicken marinates, preheat your grill to medium-high heat. If using a grill pan, heat it over medium-high heat until hot.
Cook the Chicken: Take the chicken from the marinade, allowing any excess to drain. Arrange the chicken thighs on the preheated grill. Cook for approximately 5-7 minutes on each side, or until the chicken is fully cooked and has appealing grill marks. Ensure the internal temperature reaches 165°F (74°C).
Rest the Chicken: Transfer the grilled chicken to a plate and let it rest for 5 minutes to allow the juices to redistribute.
Garnish and Serve: Slice the chicken into strips if desired. Garnish with chopped green onions and extra cilantro before serving. This grilled chicken pairs wonderfully with jasmine rice, vermicelli noodles, or a fresh salad.