Heat the oil in a wok over a medium-high heat and add the lemongrass, ginger, shallots and chillies. Stir-fry until fragrant, then add the tomatoes, lime leaves and aubergine. Cook until the aubergine is almost soft. Add the sweetcorn, green beans, sugar and salt and continue to stir-fry until the vegetables are tender crisp. Leave to cool a little before scattering with basil leaves.