Preheat oven to 425ºF. Spread bread on a baking sheet and drizzle with olive oil and 1/2 tsp. salt; toss to coat. Bake for 10 to 13 minutes, or until edges are golden brown.
While bread toasts, prepare Panzanella Dressing by combining all ingredients (olive oil through black pepper) in a large serving bowl; stir with a whisk. Add red onion and let sit for 10 minutes.
Add toasted bread, tomatoes, sliced peaches, and basil to bowl with dressing; toss to coat. Let sit for at least 30 minutes. Shave the Castello Havarti Cheese on top of the salad, and additional basil, if desired, right before serving.