Step 1Spread the bread cubes on a baking sheet and leave them out overnight to dry.
Step 2In a large bowl, combine the bread, tomatoes, vinegar and oil. Toss to mix. Let stand 30 minutes, tossing occasionally, until the bread is softened but not soggy.
Step 3Add the cucumber, onion, olives and arugula and toss to combine. Season with salt and pepper to taste. Add more vinegar if desired. Just before serving, crumble the pancetta over the top.