Place a box grater into a large bowl. Using the side of the grater with the largest holes, grate the tomatoes until you're left with just the skin — discard this.
Place a sieve over another bowl and pour the grated tomatoes into it. Let the tomatoes sit for 5 minutes to allow any excess water/juice to drain through.
While the tomatoes drain, spray the slices of sourdough with low-calorie cooking spray. Toast in a dry frying pan for a minute on each side until golden.
Once the bread is toasted, cut the garlic in half and rub each half over the slices of toasted bread.
Add the drained tomatoes into a mixing bowl. Then add in 1/2 tbsp extra virgin olive oil, the red wine vinegar, and a pinch of salt. Mix well to combine.
To serve, spoon the tomatoes over the toasted bread, then sprinkle with some freshly chopped chives and a drizzle of the remaining olive oil.