2 garlic cloves, finely grated
½ cup sliced hot pickled peppers (such as banana peppers), plus 1 Tbsp. pickle brine
1 Tbsp. stone-ground or whole grain mustard
1½ tsp. kosher salt
1½ lb. plum tomatoes (6–7 medium), sliced ½" thick
8 oz. thick-cut bacon (about 6 slices), cut into 1½" pieces
1 (10–12-oz.) loaf crusty multigrain bread, sliced ¾" thick
3 large slightly firm peaches (about 1¼ lb.), preferably freestone, halved, pitted
Whisk garlic, pickle brine, mustard, and salt in a large bowl to combine. Add tomatoes and pickled peppers and gently toss to combine. Let sit, tossing occasionally, while you cook the bacon, bread, and peaches.
Arrange bacon in a cold large cast-iron skillet and set over medium heat. Cook, stirring occasionally, until mostly crisp (there can still be a few soft, chewy spots if you’re into that sort of thing), about 10 minutes. Transfer bacon to paper towels to drain. Pour bacon fat into a small bowl; set aside. Wipe out skillet.
Heat 2 Tbsp. reserved bacon fat in same skillet. Working in batches and adding more bacon fat as needed, toast bread until golden (a few char marks are fine), about 2 minutes per side. Transfer to paper towels to drain. Wipe out skillet.
Heat another 1 Tbsp. bacon fat (if you’ve run out, use vegetable or olive oil) in same skillet and cook peach halves, cut side down, until lightly charred, about 3 minutes. Transfer to a cutting board; let sit until cool enough to handle. Slice each half in half again or into thirds and add to bowl with tomatoes. Tear toasted bread into 1"–1½" pieces and add to bowl. Add bacon and toss gently to combine and saturate bread with juices collected in bowl.
Transfer panzanella to a platter or individual bowls to serve.