Preheat the oven to 400 degrees.
For the crust, combine the oats, flour, and salt in a food processor. Process until the oats are broken down into flour.
Add the remaining crust ingredients. If the dough is too dry to form a ball, add the water a little bit at a time.
Roll out the crust between two pieces of wax paper. Transfer the crust to and 8-inch pie pan.
For the filling, stir together the blueberries, apples, and maple syrup. Pour the mixture into the crust.
Bake the pie for 15 minutes at 400 degrees. While it’s baking, stir together the crumb topping ingredients in a large bowl.
After the pie has baked for 15 minutes, remove it from the oven and add the crumb topping. Turn the oven down to 375 and bake for another 20-30 minutes. The pie is done when the apples are soft and the crumb topping is beginning to brown.
Let the pie cool before cutting.