Add the lime juice, fish sauce, sugar, oil, soy sauce, garlic, lemongrass, and onions to a blender or food processor, and blend till you get a smooth paste.
Toss the chicken well with the marinade, till well coated. Let it sit for a minimum of 10 minutes, but 30-45 minutes is ideal.
Add a teaspoon of cooking oil in a frying pan. Let it get hot, then add the chicken in batches, turning evenly to ensure it cooks on all sides, for around 7-10 minutes.