Preheat the oven to 170C and toast the cubed bread for about 20 mins until golden. Leave to cool. Chop the cucumber, onion and tomatoes and place in a large bowl. Add the bread and mix well. Whisk the olive oil, vinegar, capers, sugar and some salt and pepper together. Add to the bowl and give it a good stir. Cover and leave in fridge overnight. Add shredded basil just before serving.