Preheat oven to 425 degrees F. Spray a 9" square baking dish or pan with nonstick cooking spray.
For the filling, mix in the sugar, flour, cinnamon, lemon zest and salt in a large bowl. Add the peach slices and lemon juice. Toss until well combined. Pour into the prepared dish and bake until bubbly, about 15 mins.
Meanwhile, for the topping, place the flour, 1/2 cup of sugar, baking powder and salt in a medium bowl. Mix well. Cut in the butter with a pastry blender or 2 knives until coarse crumbs form. Add 1/2 cup water, stirring just until the dry ingredients are moistened.
Remove the dish from the oven. Drop the dough by heaping tablespoons onto the peach filling. Sprinkle the remaining sugar over the top of the dough. Bake until the topping is golden brown, about 20 minutes longer. Serve warm or at room temperature.