Lightly coat a 4 1/2 x 8 1/2 inch loaf pan with nonstick spray. Preheat oven to 350.
In a large bowl, whisk the bananas with the egg. Whisk in the maple syrup and yogurt until well combined. Last, whisk in the vanilla extract and oil.
Sprinkle the baking soda, cinnamon, and salt as evenly over the top as you can.. With a rubber spatula or wooden spoon stir to combine. Sprinkle the flour evenly over the top, then gently and patiently stir it in, just until the flour disappears. The batter will be lumpy and shaggy.
Add the toasted walnuts and 3/4 cup of blueberries; gently fold to combine.
Scrape the mixture into the prepared pan and smooth the top. Sprinkle remaining 1/4 cup blueberries over the top. Bake for 35 minutes, then check the color of the bread. If it is browning too quickly at the corners, loosely tent the pan with aluminum foil. Continue baking for 24-35 minutes additional, or until the center comes out without any wet batter clinging to it.
Allow to cool for 15 minutes. Remove the bread from the pan and transfer to the rack to finish cooling completely.
Notes
I used vegetable oil instead of coconut oil; you can also use canola oil.
I toast walnuts in the microwave, but you can also toast in the oven.