PREHEAT oven to 350F and spray a 9 × 5-in. loaf pan with oil.
BATTER: Rub sugar and lemon zest in a large bowl with hands to release the natural oil. Whisk in flour, baking powder and salt.
WHISK eggs, oil, buttermilk and vanilla in a medium bowl. Stir into flour mixture until just combined. Stir in lemon juice. Pour into pan and bake until a tester inserted into centre of loaf comes out clean, 60 to 70 min.
GLAZE Whisk icing sugar and lemon juice in a small, microwave-safe bowl. Reserve ¼ cup of the glaze. Stir 1 tbsp water into remaining glaze and microwave for 30 sec until warm. Brush over hot loaf. Allow loaf to cool for 10 min in pan. Remove to a rack. Brush with reserved glaze and let cool completely.