Preheat oven to 350 degrees F (175 degrees C). Grease a 9x5-inch bread pan.
Whisk squash, honey, blueberry syrup, oil, egg, and vanilla extract together in a bowl. Mix all-purpose flour, whole wheat flour, baking soda, baking powder, and salt together in a separate bowl; add blueberries and walnuts. Stir flour mixture into squash mixture just until combined; pour into prepared bread pan.
Bake in the preheated oven until the top is brown and a toothpick inserted in the center comes out clean, about 1 hour.
