Heat the grill to hot and char the peppers underneath, turning occasionally until blistered and coloured all over. Remove and place in a plastic bag, making sure you tie it securely. Leave to cool.
Meanwhile, de-seed the tomatoes and dice roughly. Remove the peppers from the bag and peel off the skins and discard the stalks and seeds. Dice roughly and mix with the tomatoes and minced garlic. Transfer to a large frying pan and heat over a medium-low heat until some of the water has evaporated away and you have a slightly dried mixture.
Adjust the seasoning as necessary with the caster sugar, salt and pepper. Stir in the chopped parsley and olive oil then transfer to a bowl. Cover and chill until cold.
When ready to serve, spoon into serving bowls and garnish with pinches of the ground cumin and some coriander leaves.