Heat a large wok with 4 tablespoons oil. Add the garlic and chicken and stir-fry for about 8 - 10 minutes until the chicken is cooked through.
Add the onions and fish sauce and stir fry for about 5 minutes.
Add the rest of the ingredients and cook for about 5 minutes until the vegetables are cooked but not soggy.
Serve immediate with hot steamed rice.