Peel the avocado and quarter it. Cut it into 1cm-wide strips and then into similar-sized cubes. Put the avocado pieces into a mixing bowl.
Cut the cherry tomatoes into quarters and add to the avocado.
Cut the cucumber into quarters lengthwise and chop into 1cm wedges. Add to the bowl along with the thinly sliced onion.
The bread should be dry and biscuit-like. Cut it into bite-sized pieces and add it to the rest of the ingredients.
Dress with the olive oil and vinegar,season with salt and pepper and toss well.
Place in the refrigerator,covered,for an hour.
To serve,add the parsley and toss well before arranging on plates.