Preheat the oven to 350°F. Prep 4 ramekins with cooking spray or butter. Place on a baking sheet lined with foil because things will get bubbly! Prep 4 ramekins with cooking spray or butter. Place on a baking sheet lined with foil.
To make the filling: Using a spoon, toss the blueberries, tapioca flour, maple syrup, and vanilla in a medium bowl. Set aside.
To make the crumble topping: Combine oats, walnuts, brown sugar, salt, and cinnamon. Using a pastry cutter, fork or your hands, cut the butter into the oat mixture until it takes on a crumb-like appearance.
Heap 1 cup of blueberries into each of the ramekins. Top each with two tablespoons of the crumble topping.
Bake until juices bubble and the crumble topping becomes golden brown, about 30-35 minutes. Let cool slightly. Serve warm.Optional: Enjoy with a dollop of vanilla yogurt or whipped cream.