Saute Garlic, Onions, and Ginger in a little oil. Add chicken and saute for 5 minutes. Add water and let all the food boil. Once it has boiled add Fish Sauce. Simmer at a low heat until the chicken is thoroughly cooked. You'll know it is cooked when the chicken comes off the bone.
When the soup is ready, garnish with green onions.
Add salt, pepper and soy sauce to your own liking.