Preheat the oven to 190°C. Spread the bread out over two-thirds of a large roasting tin. Toss the yellow pepper chunks in 1 tbsp oil and put in a single layer on the remaining third of the tin. Roast in the oven for 20 minutes or until golden. Remove and leave to cool for a few minutes.
While the bread and peppers are roasting, put the remaining oil in a large serving bowl and whisk in the vinegar, caster sugar and a little ground black pepper. Add the onion slices and toss well to coat in the dressing, then add the tomatoes and capers, and mix together.
Add the bread and yellow peppers to the bowl. Scatter with the torn basil, then mix well. Cover and chill until you are ready to serve. Drain the mini mozzarella cheeses and arrange over the top of the salad before serving.
For mozzarella, use a drained 200g can tuna in olive oil, flaked, or a 185g can skinless boneless sardines.
If you can't find mini mozzarella, buy two 125g packs mozzarella and cut into pieces. * You can buy the 50 per cent less fat mozzarella, if you prefer.
The salad can be chilled for several hours, or even overnight.