Preheat oven to 350 deg F. Loaf tin butter and flour. Whisk flour, baking powder and salt in medium bowl.
Using your fingers, rub sugar with lemon zest until sugar is moist. Add yogurt thinned a little with water, veg oil, eggs, and vanilla extract. Whisk to blend.
Fold in dry ingredients until just combined. Pour batter into pan. Bake 45-50 mins