Remove the tomatoes from the vine and wash. Heat the griddle pan, then drizzle the bread with olive oil and griddle the slices for 2 minutes on each side. Leave to cool.
In a small bowl, whisk together the oil, balsamic vinegar, mustard and sugar. Season to taste. Thinly slice the tomatoes and toss with the basil, red onion and the dressing.
Break the ciabatta slices into bite-sized pieces and layer with the tomato salad. Finish with a drizzle of the balsamic vinegar to serve.