Preparation Preheat oven to 300°F with rack in middle. Spread out bread in a 4-sided sheet pan and toast in oven, stirring occasionally, until pale golden, 20 to 25 minutes. Cool completely. While bread cools, halve cucumber lengthwise, then core and thinly slice. Toss together bread, cucumber, remaining ingredients, 1/4 tsp salt, and 1/2 tsp pepper and let stand, tossing occasionally, 30 minutes. Season with additional oil, vinegar, salt, and pepper.
Preparation Preheat oven to 300°F with rack in middle. Spread out bread in a 4-sided sheet pan and toast in oven, stirring occasionally, until pale golden, 20 to 25 minutes. Cool completely. While bread cools, halve cucumber lengthwise, then core and thinly slice. Toss together bread, cucumber, remaining ingredients, 1/4 tsp salt, and 1/2 tsp pepper and let stand, tossing occasionally, 30 minutes. Season with additional oil, vinegar, salt, and pepper.