To make the stir-fry sauce, put the soy sauce, oyster sauce and sugar in a small jug and stir together to combine. Set aside until needed.
Heat the oil over a moderate heat in a wok or frying pan. Add the eggplant and toss constantly for 3–4 minutes until the eggplant is almost cooked and slightly browned.
Add the garlic and chilli to the pan, tossing for a further 1 minute, but be careful that the garlic does not burn – this can happen very quickly. Reduce the heat slightly, then pour in the stir-fry sauce and stir well until the eggplant is coated in the sauce. Take the wok off the heat and toss in the chopped coriander. Serve immediately, garnished with sprigs of fresh coriander.
You can easily adjust the heat of this dish. If you want it to be spicy, retain the seeds and membranes of the chilli(es), but for a milder flavour, you can remove them.