Preheat the oven to 375 degrees, and lightly grease an 8 x 11-inch or similar size (2 to 2-1/2 quart) baking dish.
In a large bowl, mix together the oats, 1/4 cup of the coconut, 1/4 cup of the walnuts, baking powder, cinnamon, and salt.
In another bowl, whisk together the maple syrup, milk, egg, butter, and vanilla.
Sprinkle half of the berries over the bottom of the baking dish. Cover the fruit evenly with the dry oat mixture. Slowly drizzle the milk mixture over the oats.
Then, scatter the remaining blueberries, coconut, and walnuts over the top.
Bake for 30 to 35 minutes or until the oat mixture has just set in the center and the top is beginning to brown.
Remove from the oven and let cool for a few minutes.
This may be eaten immediately or made ahead and reheated. Store leftovers in the refrigerator.