Place the aubergines under a grill and cook until the skins are black and blistered and the flesh feels soft inside. Put them in a colander and peel them as soon as they are cool enough to handle; then squeeze out the juice.
Chop or mash the aubergines or purée them in a food processor. Add the garlic, mint, oil and syrup or juice, season to taste with salt and pepper and mix well. Fold in the tomatoes gently and serve cold.