Using a sharp knife, trim the crust from the bread, and discard the crust. Tear the bread into rough bite-sized pieces. You should have about 4 loosely packed cups' worth (about 1 L). Dump the bread out onto a rimmed baking sheet, and drizzle it with olive oil. Toss to coat. Don't worry if the pieces aren't evenly oiled; that's okay. Bake until crispy and golden in spots, shaking the pan once, 8 to 10 minutes.
Meanwhile, put about one-third of the cherries in a small bowl, and crush them lightly with a fork, so that they release their juices. You don't want to mash them completely; just smash them a bit.
When the bread is nicely toasted, turn it out into a large bowl. While it is still hot, add the garlic, and toss well. Set aside to cool for a minute or two. Then add the cherries, both the smashed ones and the not-smashed ones, and toss. Add 2 teaspoons balsamic vinegar and toss again. Add 1 tablespoon olive oil and a pinch or two of salt and toss again.
Taste, and adjust the vinegar, oil, and salt as needed: if you taste the bread and the cherries separately, they should each taste good alone. When you're satisfied with the flavour, add about 2 handfuls of arugula and toss one last time. Finish with a generous amount of crumbled goat cheese and a few grinds of the pepper mill, and serve.