Preheat oven to 350°F. Using an electric mixer, cream the butter and sugars until light and fluffy. Add the eggs, vanilla and salt and beat well. In a large bowl, combine baking powder, baking soda. In dry skillet, toast walnuts over medium-high heat for 1 to 2 minutes. In large bowl, combine all-purpose flour, baking powder, baking soda and salt.Whisk to combine. In medium bowl, combine sugar, lemon zest, buttermilk, eggs, vanilla, melted butter and oil. Whisk just to combine. Make a well in center of dry ingredients. Add liquid ingredients and mix gently just to combine; do not over-mix. Gently fold in walnuts and blueberries Pour batter into a greased and floured 8 x 4-inch loaf pan. Bake in preheated oven for 55 to 60 minutes or until tester inserted in center comes out clean. Cool on rack for 20 minutes; remove from pan, cool to room temperature.
To make the glaze combine sugar and lemon juice in small saucepan. Bring to boil over high heat, then reduce heat and continue stirring until sugar dissolves. Brush glaze over bread while still warm