Preheat oven to 350 degrees F. Toast walnuts.In large bowl combine flour,baking powder,baking soda,and salt. Whisk together and set aside. In medium bowl combine sugar,lemon zest, buttermilk, eggs, vanilla, melted butter and oil. Stir to combine. Make a well in centre of dry ingredients.Add wet ingredients and mix gently to combine.Do not overmix. Gently fold in berries and nuts. Pour into greased and floured loaf pan.Bake 55 to 60 mins.Cool before glazing.
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Glaze; Bring sugar and lemon juice to boil in small saucepan. Stir till sugar is dissolved. When loaf is cool brush warm glaze over all.