Preheat your oven to 350°F (175°C).
Grease a 9x5-inch loaf pan with butter or nonstick spray.
In a large bowl, whisk together flour, baking powder, and salt until well combined.
In another bowl, beat together softened butter and sugar until light and fluffy, about 3 minutes.
Incorporate eggs one at a time into the butter-sugar mix.
Pour in lemon zest, juice, and vanilla extract.
Gradually fold in your dry ingredients until just combined, being careful not to overmix.
Gently fold in chopped rhubarb until evenly distributed throughout the batter.
Pour the batter into your prepared loaf pan.
Bake for 50-60 minutes or until a toothpick inserted comes out clean.
While your loaf cools, whisk powdered sugar with lemon juice until smooth.