Make sure your bread is dry so the croutons won't get soggy when tossed with the dressing. If you're using the fresh bread, bake the bread cubes at 350º for 5 minutes. Serve this salad immediately, while the bread is still crunchy.
To prepare vinaigrette, combine first 6 ingredients; stir with a whisk.
To prepare salad, combine cucumber and next 7 ingredients (cucumber through tuna) in a large bowl. Add bread. Drizzle with vinaigrette; toss gently to combine.
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