Preheat oven to 375 degrees. In a large bowl, toss peaches, sugar, lemon juice, and flour to combine. Transfer to an 8-inch square (or other shallow 2-quart) baking dish.
In a food processor, pulse bread until coarse crumbs form; sprinkle over fruit mixture, and dot with butter. Cover tightly with aluminum foil.
Bake until fruit mixture is bubbling, 25 to 30 minutes. Remove foil, and continue baking until topping is golden, 10 to 15 minutes more. Let sit at least 10 minutes. Serve with whipped cream, if desired.