Heat the oil in a wok or large frying pan. Stir-fry the garlic over a medium heat for 1–2 minutes or until lightly browned. Add the chillies, chicken, onion, stock or water, fish sauce and oyster sauce. Stir-fry for 4–5 minutes or until the meat is cooked.
Add the tomatoes and basil leaves and stir-fry until the basil begins to wilt. Taste and adjust the seasoning.
Spoon on to a serving plate.