In a large bowl, combine all the filling ingredients. Pour into the skillet and set aside.
Place the walnuts in a food processor fitted with the steel blade. Pulse a few times to finely chop, but do not turn into flour. Transfer to a mixing bowl and add the almond flour, tapioca flour, cinnamon, and salt. Add the coconut oil and maple syrup. Use your fingers to work the oil and syrup into the dry ingredients and form a crumbly dough. Sprinkle the topping evenly over the fruit filling.