Preheat oven to 375°F. In a large bowl, toss peaches with sugar, cornstarch, vanilla, cinnamon, and lemon juice. Pour into a greased 9x9 inch baking dish.
In a separate bowl, whisk together gluten free flour, sugar, baking powder, and salt. Cut in cold butter using a pastry cutter or fork until mixture resembles coarse crumbs.
Pour boiling water over the flour mixture and stir just until combined into a thick batter. The dough will be sticky.
Drop spoonfuls of the batter over the peach filling, covering most of the surface but leaving some gaps for steam to escape.
Bake for 40-45 minutes until topping is golden brown and fruit is bubbling around the edges.
Let cool for 15 minutes before serving warm with vanilla ice cream or whipped cream.