Place in a cold oven and turn up the heat to 350°F, allowing the
bread to come up to temperature along with the oven. Bake until
the bread is just golden, flipping the bread over after 10 minutes so
it toasts evenly. Be patient: it might take a little while (anywhere
from 10 to 20 minutes, depending on how quickly the oven heats).
Allow the bread to cool so you can handle it. Then rub each
piece with some garlic*.
With your hands, break the bread into 1-inch chunks into a large
bowl. In a separate bowl, dilute the ⅓ cup of balsamic vinegar
with ⅔ cup cold water, stirring to combine. Drizzle the balsamic
mixture over the bread, stirring the bread as you do that so all the
pieces get evenly coated.
Add the tuna, tomatoes, olives, capers, and parsley to the bowl
with the bread. Add a good glug of olive oil and a sprinkling of salt
and stir. Taste the salad and, inevitably, you’ll need to adjust it.
Add more salt, balsamic, and/or oil until it tastes fantastic.
You can serve it right away or allow it to sit at room
temperature for an hour or two (this gives time for the flavors to
develop).
* Press down while you do this, so the rough bread exterior
breaks down the garlic as you rub it. You get more garlic flavor
that way.