Preheat the oven to 350°F (190°C). Butter a 9x11 baking dish or a 10” round skillet that is at least 2” deep.
In a mixing bowl, gently toss together the bananas, brown sugar, cinnamon, allspice, cornstarch, and vanilla extract. Be careful not to break up the bananas. Pour the mixture into the prepared baking dish.
In a separate bowl, combine the sugar, gluten-free flour, baking powder, and salt. Mix well. Add the cold butter and use a fork or pastry cutter to cut the butter into the dry ingredients until it forms pea-sized crumbs.
Stir in the vanilla extract, buttermilk, walnuts, and oats until everything is well incorporated.
Using an ice cream scoop, drop spoonfuls of batter evenly over the banana filling.
Place the cobbler in the oven and bake for 35-40 minutes, or until the top is golden brown and the filling is bubbly.
Remove the cobbler from the oven and allow it to cool for about 5 minutes. Drizzle with caramel sauce before serving.
