For the tomato relish, place a medium saucepan over a medium low heat. Add olive oil and when hot, add the onion and sauté for a few minutes. Add the garlic, reduce heat slightly and cook for 4-5 minutes, stirring occasionally, until onions have softened and are starting to caramelise.
Pour in tomato passata, sugar and vinegar. Increase heat and bring to the boil. Reduce the heat and simmer for 5 minutes. Add in the chopped tomatoes and cook for a further 5 minutes or until the tomatoes have broken down. Season to taste. Remove from heat and allow to cool.
To cook the sausages, place them in a hot pan, drizzled with a little olive oil and cook for approximately 10-12 minutes or until cooked through, turning occasionally.
For the bread, split down the middle and fill with a little bit of mozzarella cheese. Place under a preheated grill for 1-2 minutes or until the cheese has melted and the bun is warm and the edges are golden.
To assemble, fill each bun with a piece of lettuce and a few carrot ribbons. Place a sausage in and top with generous spoonful’s of tomato relish and a sprinkle of finely chopped chives.
To serve, arrange on a serving plate with extra tomato relish in a bowl on the side.