Arrange bread cubes in a single layer on a baking sheet. Bake at 400° for 8 minutes or until toasted; cool.
Combine tomato and next 6 ingredients (through garlic) in a large bowl. Combine vinegar, oil, sugar, black pepper, and salt. Add vinegar mixture to tomato mixture; toss well. Cover and let stand 1 hour.
Add bread cubes, arugula, and Garlic-Rubbed Flank Steak to tomato mixture; toss gently to coat. Serve immediately.